diff --git a/src/doc/tutorial.md b/src/doc/tutorial.md
index 2e6a0ef7e5b..c2469e0c171 100644
--- a/src/doc/tutorial.md
+++ b/src/doc/tutorial.md
@@ -2519,7 +2519,7 @@ of type `ABC` can be randomly generated and converted to a string:
 #[deriving(Eq)]
 struct Circle { radius: f64 }
 
-#[deriving(Rand, ToStr)]
+#[deriving(Rand, Show)]
 enum ABC { A, B, C }
 ~~~
 
diff --git a/src/libcollections/btree.rs b/src/libcollections/btree.rs
index 13b39da0756..cc6a5eda759 100644
--- a/src/libcollections/btree.rs
+++ b/src/libcollections/btree.rs
@@ -18,7 +18,8 @@
 ///a length (the height of the tree), and lower and upper bounds on the
 ///number of elements that a given node can contain.
 
-use std::vec::OwnedVector;
+use std::fmt;
+use std::fmt::Show;
 
 #[allow(missing_doc)]
 pub struct BTree<K, V> {
@@ -106,11 +107,10 @@ impl<K: TotalOrd, V: TotalEq> TotalOrd for BTree<K, V> {
     }
 }
 
-impl<K: ToStr + TotalOrd, V: ToStr> ToStr for BTree<K, V> {
+impl<K: fmt::Show + TotalOrd, V: fmt::Show> fmt::Show for BTree<K, V> {
     ///Returns a string representation of the BTree
-    fn to_str(&self) -> ~str {
-        let ret = self.root.to_str();
-        ret
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        self.root.fmt(f)
     }
 }
 
@@ -235,15 +235,15 @@ impl<K: TotalOrd, V: TotalEq> TotalOrd for Node<K, V> {
     }
 }
 
-impl<K: ToStr + TotalOrd, V: ToStr> ToStr for Node<K, V> {
+impl<K: fmt::Show + TotalOrd, V: fmt::Show> fmt::Show for Node<K, V> {
     ///Returns a string representation of a Node.
     ///Will iterate over the Node and show "Key: x, value: y, child: () // "
     ///for all elements in the Node. "Child" only exists if the Node contains
     ///a branch.
-    fn to_str(&self) -> ~str {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match *self {
-            LeafNode(ref leaf) => leaf.to_str(),
-            BranchNode(ref branch) => branch.to_str()
+            LeafNode(ref leaf) => leaf.fmt(f),
+            BranchNode(ref branch) => branch.fmt(f),
         }
     }
 }
@@ -401,10 +401,14 @@ impl<K: TotalOrd, V: TotalEq> TotalOrd for Leaf<K, V> {
 }
 
 
-impl<K: ToStr + TotalOrd, V: ToStr> ToStr for Leaf<K, V> {
+impl<K: fmt::Show + TotalOrd, V: fmt::Show> fmt::Show for Leaf<K, V> {
     ///Returns a string representation of a Leaf.
-    fn to_str(&self) -> ~str {
-        self.elts.iter().map(|s| s.to_str()).to_owned_vec().connect(" // ")
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        for (i, s) in self.elts.iter().enumerate() {
+            if i != 0 { if_ok!(write!(f.buf, " // ")) }
+            if_ok!(write!(f.buf, "{}", *s))
+        }
+        Ok(())
     }
 }
 
@@ -618,13 +622,14 @@ impl<K: TotalOrd, V: TotalEq> TotalOrd for Branch<K, V> {
     }
 }
 
-impl<K: ToStr + TotalOrd, V: ToStr> ToStr for Branch<K, V> {
+impl<K: fmt::Show + TotalOrd, V: fmt::Show> fmt::Show for Branch<K, V> {
     ///Returns a string representation of a Branch.
-    fn to_str(&self) -> ~str {
-        let mut ret = self.elts.iter().map(|s| s.to_str()).to_owned_vec().connect(" // ");
-        ret.push_str(" // ");
-        ret.push_str("rightmost child: ("+ self.rightmost_child.to_str() +") ");
-        ret
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        for (i, s) in self.elts.iter().enumerate() {
+            if i != 0 { if_ok!(write!(f.buf, " // ")) }
+            if_ok!(write!(f.buf, "{}", *s))
+        }
+        write!(f.buf, " // rightmost child: ({}) ", *self.rightmost_child)
     }
 }
 
@@ -672,11 +677,10 @@ impl<K: TotalOrd, V: TotalEq> TotalOrd for LeafElt<K, V> {
     }
 }
 
-impl<K: ToStr + TotalOrd, V: ToStr> ToStr for LeafElt<K, V> {
+impl<K: fmt::Show + TotalOrd, V: fmt::Show> fmt::Show for LeafElt<K, V> {
     ///Returns a string representation of a LeafElt.
-    fn to_str(&self) -> ~str {
-        format!("Key: {}, value: {};",
-            self.key.to_str(), self.value.to_str())
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f.buf, "Key: {}, value: {};", self.key, self.value)
     }
 }
 
@@ -715,12 +719,12 @@ impl<K: TotalOrd, V: TotalEq> TotalOrd for BranchElt<K, V> {
     }
 }
 
-impl<K: ToStr + TotalOrd, V: ToStr> ToStr for BranchElt<K, V> {
-    ///Returns string containing key, value, and child (which should recur to a leaf)
-    ///Consider changing in future to be more readable.
-    fn to_str(&self) -> ~str {
-        format!("Key: {}, value: {}, (child: {})",
-            self.key.to_str(), self.value.to_str(), self.left.to_str())
+impl<K: fmt::Show + TotalOrd, V: fmt::Show> fmt::Show for BranchElt<K, V> {
+    /// Returns string containing key, value, and child (which should recur to a
+    /// leaf) Consider changing in future to be more readable.
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f.buf, "Key: {}, value: {}, (child: {})",
+               self.key, self.value, *self.left)
     }
 }
 
diff --git a/src/libcollections/enum_set.rs b/src/libcollections/enum_set.rs
index 0de6eaf53dd..2bd8cbf03e9 100644
--- a/src/libcollections/enum_set.rs
+++ b/src/libcollections/enum_set.rs
@@ -15,7 +15,7 @@
 
 use std::num::Bitwise;
 
-#[deriving(Clone, Eq, Hash, ToStr, Encodable, Decodable)]
+#[deriving(Clone, Eq, Hash, Show, Encodable, Decodable)]
 /// A specialized Set implementation to use enum types.
 pub struct EnumSet<E> {
     // We must maintain the invariant that no bits are set
diff --git a/src/libcollections/hashmap.rs b/src/libcollections/hashmap.rs
index fe56dbdd2f1..877f2b30009 100644
--- a/src/libcollections/hashmap.rs
+++ b/src/libcollections/hashmap.rs
@@ -606,10 +606,6 @@ impl<A: fmt::Show + Hash + Eq, B: fmt::Show> fmt::Show for HashMap<A, B> {
     }
 }
 
-impl<K: fmt::Show + Hash + Eq, V: fmt::Show> ToStr for HashMap<K, V> {
-    fn to_str(&self) -> ~str { format!("{}", *self) }
-}
-
 /// HashMap iterator
 #[deriving(Clone)]
 pub struct Entries<'a, K, V> {
@@ -888,10 +884,6 @@ impl<A: fmt::Show + Hash + Eq> fmt::Show for HashSet<A> {
     }
 }
 
-impl<A: fmt::Show + Hash + Eq> ToStr for HashSet<A> {
-    fn to_str(&self) -> ~str { format!("{}", *self) }
-}
-
 impl<K: Eq + Hash> FromIterator<K> for HashSet<K> {
     fn from_iterator<T: Iterator<K>>(iter: &mut T) -> HashSet<K> {
         let (lower, _) = iter.size_hint();
diff --git a/src/libcollections/lru_cache.rs b/src/libcollections/lru_cache.rs
index ec387df7215..b5e44cda665 100644
--- a/src/libcollections/lru_cache.rs
+++ b/src/libcollections/lru_cache.rs
@@ -37,10 +37,11 @@
 //! assert!(cache.get(&2).is_none());
 //! ```
 
+use std::cast;
 use std::container::Container;
 use std::hash::{Hash, sip};
+use std::fmt;
 use std::ptr;
-use std::cast;
 
 use HashMap;
 
@@ -217,36 +218,32 @@ impl<K: Hash + Eq, V> LruCache<K, V> {
     }
 }
 
-impl<A: ToStr + Hash + Eq, B: ToStr> ToStr for LruCache<A, B> {
+impl<A: fmt::Show + Hash + Eq, B: fmt::Show> fmt::Show for LruCache<A, B> {
     /// Return a string that lists the key-value pairs from most-recently
     /// used to least-recently used.
-    #[inline]
-    fn to_str(&self) -> ~str {
-        let mut acc = ~"{";
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        if_ok!(write!(f.buf, r"\{"));
         let mut cur = self.head;
         for i in range(0, self.len()) {
-            if i > 0 {
-                acc.push_str(", ");
-            }
+            if i > 0 { if_ok!(write!(f.buf, ", ")) }
             unsafe {
                 cur = (*cur).next;
                 match (*cur).key {
                     // should never print nil
-                    None => acc.push_str("nil"),
-                    Some(ref k) => acc.push_str(k.to_str())
+                    None => if_ok!(write!(f.buf, "nil")),
+                    Some(ref k) => if_ok!(write!(f.buf, "{}", *k)),
                 }
             }
-            acc.push_str(": ");
+            if_ok!(write!(f.buf, ": "));
             unsafe {
                 match (*cur).value {
                     // should never print nil
-                    None => acc.push_str("nil"),
-                    Some(ref value) => acc.push_str(value.to_str())
+                    None => if_ok!(write!(f.buf, "nil")),
+                    Some(ref value) => if_ok!(write!(f.buf, "{}", *value)),
                 }
             }
         }
-        acc.push_char('}');
-        acc
+        write!(f.buf, r"\}")
     }
 }
 
diff --git a/src/libextra/json.rs b/src/libextra/json.rs
index 4cc210aaa6c..d438b00b992 100644
--- a/src/libextra/json.rs
+++ b/src/libextra/json.rs
@@ -240,7 +240,7 @@ use std::io;
 use std::io::MemWriter;
 use std::num;
 use std::str;
-use std::to_str;
+use std::fmt;
 
 use serialize::Encodable;
 use serialize;
@@ -1576,18 +1576,16 @@ impl<A:ToJson> ToJson for Option<A> {
     }
 }
 
-impl to_str::ToStr for Json {
+impl fmt::Show for Json {
     /// Encodes a json value into a string
-    fn to_str(&self) -> ~str {
-        let mut s = MemWriter::new();
-        self.to_writer(&mut s as &mut io::Writer).unwrap();
-        str::from_utf8_owned(s.unwrap()).unwrap()
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        self.to_writer(f.buf)
     }
 }
 
-impl to_str::ToStr for Error {
-    fn to_str(&self) -> ~str {
-        format!("{}:{}: {}", self.line, self.col, self.msg)
+impl fmt::Show for Error {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f.buf, "{}:{}: {}", self.line, self.col, self.msg)
     }
 }
 
diff --git a/src/libextra/url.rs b/src/libextra/url.rs
index 41d6d95c6bb..6e0cd72e3e7 100644
--- a/src/libextra/url.rs
+++ b/src/libextra/url.rs
@@ -12,12 +12,14 @@
 
 #[allow(missing_doc)];
 
-use std::io::BufReader;
 use std::cmp::Eq;
-use collections::HashMap;
+use std::fmt;
 use std::hash::{Hash, sip};
+use std::io::BufReader;
 use std::uint;
 
+use collections::HashMap;
+
 /// A Uniform Resource Locator (URL).  A URL is a form of URI (Uniform Resource
 /// Identifier) that includes network location information, such as hostname or
 /// port number.
@@ -407,10 +409,12 @@ fn split_char_first(s: &str, c: char) -> (~str, ~str) {
     }
 }
 
-fn userinfo_to_str(userinfo: &UserInfo) -> ~str {
-    match userinfo.pass {
-        Some(ref pass) => format!("{}:{}@", userinfo.user, *pass),
-        None => format!("{}@", userinfo.user),
+impl fmt::Show for UserInfo {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self.pass {
+            Some(ref pass) => write!(f.buf, "{}:{}@", self.user, *pass),
+            None => write!(f.buf, "{}@", self.user),
+        }
     }
 }
 
@@ -437,19 +441,18 @@ fn query_from_str(rawquery: &str) -> Query {
  * println!("{}", url::query_to_str(&query));  // title=The%20Village&north=52.91&west=4.10
  * ```
  */
+#[allow(unused_must_use)]
 pub fn query_to_str(query: &Query) -> ~str {
-    let mut strvec = ~[];
-    for kv in query.iter() {
-        match kv {
-            &(ref k, ref v) => {
-                strvec.push(format!("{}={}",
-                    encode_component(*k),
-                    encode_component(*v))
-                );
-            }
-        }
+    use std::io::MemWriter;
+    use std::str;
+
+    let mut writer = MemWriter::new();
+    for (i, &(ref k, ref v)) in query.iter().enumerate() {
+        if i != 0 { write!(&mut writer, "&"); }
+        write!(&mut writer, "{}={}", encode_component(*k),
+               encode_component(*v));
     }
-    return strvec.connect("&");
+    str::from_utf8_lossy(writer.unwrap()).into_owned()
 }
 
 /**
@@ -784,74 +787,64 @@ impl FromStr for Path {
     }
 }
 
-/**
- * Converts a URL from `Url` to string representation.
- *
- * # Arguments
- *
- * `url` - a URL.
- *
- * # Returns
- *
- * A string that contains the formatted URL. Note that this will usually
- * be an inverse of `from_str` but might strip out unneeded separators;
- * for example, "http://somehost.com?", when parsed and formatted, will
- * result in just "http://somehost.com".
- */
-pub fn to_str(url: &Url) -> ~str {
-    let user = match url.user {
-        Some(ref user) => userinfo_to_str(user),
-        None => ~"",
-    };
+impl fmt::Show for Url {
+    /**
+     * Converts a URL from `Url` to string representation.
+     *
+     * # Arguments
+     *
+     * `url` - a URL.
+     *
+     * # Returns
+     *
+     * A string that contains the formatted URL. Note that this will usually
+     * be an inverse of `from_str` but might strip out unneeded separators;
+     * for example, "http://somehost.com?", when parsed and formatted, will
+     * result in just "http://somehost.com".
+     */
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        if_ok!(write!(f.buf, "{}:", self.scheme));
 
-    let authority = if url.host.is_empty() {
-        // If port is Some, we're in a nonsensical situation. Too bad.
-        ~""
-    } else {
-        match url.port {
-            Some(ref port) => format!("//{}{}:{}", user, url.host, *port),
-            None => format!("//{}{}", user, url.host),
+        if !self.host.is_empty() {
+            if_ok!(write!(f.buf, "//"));
+            match self.user {
+                Some(ref user) => if_ok!(write!(f.buf, "{}", *user)),
+                None => {}
+            }
+            match self.port {
+                Some(ref port) => if_ok!(write!(f.buf, "{}:{}", self.host,
+                                                *port)),
+                None => if_ok!(write!(f.buf, "{}", self.host)),
+            }
         }
-    };
 
-    let query = if url.query.is_empty() {
-        ~""
-    } else {
-        format!("?{}", query_to_str(&url.query))
-    };
+        if_ok!(write!(f.buf, "{}", self.path));
 
-    let fragment = match url.fragment {
-        Some(ref fragment) => format!("\\#{}", encode_component(*fragment)),
-        None => ~"",
-    };
+        if !self.query.is_empty() {
+            if_ok!(write!(f.buf, "?{}", query_to_str(&self.query)));
+        }
 
-    format!("{}:{}{}{}{}", url.scheme, authority, url.path, query, fragment)
-}
-
-pub fn path_to_str(path: &Path) -> ~str {
-    let query = if path.query.is_empty() {
-        ~""
-    } else {
-        format!("?{}", query_to_str(&path.query))
-    };
-
-    let fragment = match path.fragment {
-        Some(ref fragment) => format!("\\#{}", encode_component(*fragment)),
-        None => ~"",
-    };
-
-    format!("{}{}{}", path.path, query, fragment)
-}
-
-impl ToStr for Url {
-    fn to_str(&self) -> ~str {
-        to_str(self)
+        match self.fragment {
+            Some(ref fragment) => write!(f.buf, "\\#{}",
+                                         encode_component(*fragment)),
+            None => Ok(()),
+        }
     }
 }
 
-impl ToStr for Path {
-    fn to_str(&self) -> ~str {
-        path_to_str(self)
+impl fmt::Show for Path {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        if_ok!(write!(f.buf, "{}", self.path));
+        if !self.query.is_empty() {
+            if_ok!(write!(f.buf, "?{}", self.query))
+        }
+
+        match self.fragment {
+            Some(ref fragment) => {
+                write!(f.buf, "\\#{}", encode_component(*fragment))
+            }
+            None => Ok(())
+        }
     }
 }
 
diff --git a/src/libgetopts/lib.rs b/src/libgetopts/lib.rs
index 537c2d40c66..20594105183 100644
--- a/src/libgetopts/lib.rs
+++ b/src/libgetopts/lib.rs
@@ -169,7 +169,7 @@ pub struct Matches {
 /// The type returned when the command line does not conform to the
 /// expected format. Call the `to_err_msg` method to retrieve the
 /// error as a string.
-#[deriving(Clone, Eq, ToStr)]
+#[deriving(Clone, Eq, Show)]
 #[allow(missing_doc)]
 pub enum Fail_ {
     ArgumentMissing(~str),
diff --git a/src/libnum/bigint.rs b/src/libnum/bigint.rs
index 0418c61d361..894b3794581 100644
--- a/src/libnum/bigint.rs
+++ b/src/libnum/bigint.rs
@@ -19,14 +19,14 @@ A `BigInt` is a combination of `BigUint` and `Sign`.
 use Integer;
 
 use std::cmp;
-use std::cmp::{Eq, Ord, TotalEq, TotalOrd, Ordering, Less, Equal, Greater};
-use std::num::{Zero, One, ToStrRadix, FromStrRadix};
+use std::fmt;
 use std::num::{Bitwise, ToPrimitive, FromPrimitive};
+use std::num::{Zero, One, ToStrRadix, FromStrRadix};
 use std::rand::Rng;
 use std::str;
 use std::uint;
-use std::{i64, u64};
 use std::vec;
+use std::{i64, u64};
 
 /**
 A `BigDigit` is a `BigUint`'s composing element.
@@ -121,9 +121,10 @@ impl TotalOrd for BigUint {
     }
 }
 
-impl ToStr for BigUint {
-    #[inline]
-    fn to_str(&self) -> ~str { self.to_str_radix(10) }
+impl fmt::Show for BigUint {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f.buf, "{}", self.to_str_radix(10))
+    }
 }
 
 impl FromStr for BigUint {
@@ -904,9 +905,10 @@ impl TotalOrd for BigInt {
     }
 }
 
-impl ToStr for BigInt {
-    #[inline]
-    fn to_str(&self) -> ~str { self.to_str_radix(10) }
+impl fmt::Show for BigInt {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f.buf, "{}", self.to_str_radix(10))
+    }
 }
 
 impl FromStr for BigInt {
diff --git a/src/libnum/complex.rs b/src/libnum/complex.rs
index 3755b2e43af..5ffd23aa346 100644
--- a/src/libnum/complex.rs
+++ b/src/libnum/complex.rs
@@ -11,6 +11,7 @@
 
 //! Complex numbers.
 
+use std::fmt;
 use std::num::{Zero,One,ToStrRadix};
 
 // FIXME #1284: handle complex NaN & infinity etc. This
@@ -167,12 +168,12 @@ impl<T: Clone + Num> One for Cmplx<T> {
 }
 
 /* string conversions */
-impl<T: ToStr + Num + Ord> ToStr for Cmplx<T> {
-    fn to_str(&self) -> ~str {
+impl<T: fmt::Show + Num + Ord> fmt::Show for Cmplx<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         if self.im < Zero::zero() {
-            format!("{}-{}i", self.re.to_str(), (-self.im).to_str())
+            write!(f.buf, "{}-{}i", self.re, -self.im)
         } else {
-            format!("{}+{}i", self.re.to_str(), self.im.to_str())
+            write!(f.buf, "{}+{}i", self.re, self.im)
         }
     }
 }
diff --git a/src/libnum/rational.rs b/src/libnum/rational.rs
index 5f1868b48c5..44a916c5d4e 100644
--- a/src/libnum/rational.rs
+++ b/src/libnum/rational.rs
@@ -13,6 +13,7 @@
 use Integer;
 
 use std::cmp;
+use std::fmt;
 use std::from_str::FromStr;
 use std::num::{Zero,One,ToStrRadix,FromStrRadix,Round};
 use bigint::{BigInt, BigUint, Sign, Plus, Minus};
@@ -277,10 +278,10 @@ impl<T: Clone + Integer + Ord>
 }
 
 /* String conversions */
-impl<T: ToStr> ToStr for Ratio<T> {
+impl<T: fmt::Show> fmt::Show for Ratio<T> {
     /// Renders as `numer/denom`.
-    fn to_str(&self) -> ~str {
-        format!("{}/{}", self.numer.to_str(), self.denom.to_str())
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f.buf, "{}/{}", self.numer, self.denom)
     }
 }
 impl<T: ToStrRadix> ToStrRadix for Ratio<T> {
diff --git a/src/librustc/middle/liveness.rs b/src/librustc/middle/liveness.rs
index 3b9f81adbac..7293c3a3cee 100644
--- a/src/librustc/middle/liveness.rs
+++ b/src/librustc/middle/liveness.rs
@@ -111,12 +111,12 @@ use middle::moves;
 
 use std::cast::transmute;
 use std::cell::{Cell, RefCell};
-use collections::HashMap;
+use std::fmt;
 use std::io;
 use std::str;
-use std::to_str;
 use std::uint;
 use std::vec;
+use collections::HashMap;
 use syntax::ast::*;
 use syntax::codemap::Span;
 use syntax::parse::token::special_idents;
@@ -184,12 +184,16 @@ pub fn check_crate(tcx: ty::ctxt,
     tcx.sess.abort_if_errors();
 }
 
-impl to_str::ToStr for LiveNode {
-    fn to_str(&self) -> ~str { format!("ln({})", self.get()) }
+impl fmt::Show for LiveNode {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f.buf, "ln({})", self.get())
+    }
 }
 
-impl to_str::ToStr for Variable {
-    fn to_str(&self) -> ~str { format!("v({})", self.get()) }
+impl fmt::Show for Variable {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f.buf, "v({})", self.get())
+    }
 }
 
 // ______________________________________________________________________
diff --git a/src/librustc/middle/mem_categorization.rs b/src/librustc/middle/mem_categorization.rs
index c413439cb53..0882e8eb692 100644
--- a/src/librustc/middle/mem_categorization.rs
+++ b/src/librustc/middle/mem_categorization.rs
@@ -123,7 +123,7 @@ pub enum ElementKind {
     OtherElement,
 }
 
-#[deriving(Eq, Hash)]
+#[deriving(Eq, Hash, Show)]
 pub enum MutabilityCategory {
     McImmutable, // Immutable.
     McDeclared,  // Directly declared as mutable.
@@ -273,12 +273,6 @@ pub trait Typer {
     fn upvar_borrow(&mut self, upvar_id: ty::UpvarId) -> ty::UpvarBorrow;
 }
 
-impl ToStr for MutabilityCategory {
-    fn to_str(&self) -> ~str {
-        format!("{:?}", *self)
-    }
-}
-
 impl MutabilityCategory {
     pub fn from_mutbl(m: ast::Mutability) -> MutabilityCategory {
         match m {
diff --git a/src/librustc/middle/ty.rs b/src/librustc/middle/ty.rs
index 8d88c084e99..b351b5c0cb8 100644
--- a/src/librustc/middle/ty.rs
+++ b/src/librustc/middle/ty.rs
@@ -33,10 +33,11 @@ use util::common::{indenter};
 use std::cast;
 use std::cell::{Cell, RefCell};
 use std::cmp;
+use std::fmt::Show;
+use std::fmt;
 use std::hash::{Hash, sip};
 use std::ops;
 use std::rc::Rc;
-use std::to_str::ToStr;
 use std::vec;
 use collections::{HashMap, HashSet};
 use syntax::ast::*;
@@ -128,14 +129,14 @@ pub struct mt {
     mutbl: ast::Mutability,
 }
 
-#[deriving(Clone, Eq, Encodable, Decodable, Hash, ToStr)]
+#[deriving(Clone, Eq, Encodable, Decodable, Hash, Show)]
 pub enum vstore {
     vstore_fixed(uint),
     vstore_uniq,
     vstore_slice(Region)
 }
 
-#[deriving(Clone, Eq, Hash, Encodable, Decodable, ToStr)]
+#[deriving(Clone, Eq, Hash, Encodable, Decodable, Show)]
 pub enum TraitStore {
     UniqTraitStore,             // ~Trait
     RegionTraitStore(Region),   // &Trait
@@ -196,7 +197,7 @@ pub struct ItemVariances {
     region_params: OptVec<Variance>
 }
 
-#[deriving(Clone, Eq, Decodable, Encodable)]
+#[deriving(Clone, Eq, Decodable, Encodable, Show)]
 pub enum Variance {
     Covariant,      // T<A> <: T<B> iff A <: B -- e.g., function return type
     Invariant,      // T<A> <: T<B> iff B == A -- e.g., type of mutable cell
@@ -384,11 +385,13 @@ pub struct t_box_ {
 // ~15%.) This does mean that a t value relies on the ctxt to keep its box
 // alive, and using ty::get is unsafe when the ctxt is no longer alive.
 enum t_opaque {}
-pub type t = *t_opaque;
 
-impl ToStr for t {
-    fn to_str(&self) -> ~str {
-        ~"*t_opaque"
+#[deriving(Clone, Eq, Hash)]
+pub struct t { priv inner: *t_opaque }
+
+impl fmt::Show for t {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.buf.write_str("*t_opaque")
     }
 }
 
@@ -458,7 +461,7 @@ pub struct param_ty {
 }
 
 /// Representation of regions:
-#[deriving(Clone, Eq, Hash, Encodable, Decodable, ToStr, Show)]
+#[deriving(Clone, Eq, Hash, Encodable, Decodable, Show)]
 pub enum Region {
     // Region bound in a type or fn declaration which will be
     // substituted 'early' -- that is, at the same time when type
@@ -618,13 +621,13 @@ impl Region {
     }
 }
 
-#[deriving(Clone, Eq, TotalOrd, TotalEq, Hash, Encodable, Decodable, ToStr, Show)]
+#[deriving(Clone, Eq, TotalOrd, TotalEq, Hash, Encodable, Decodable, Show)]
 pub struct FreeRegion {
     scope_id: NodeId,
     bound_region: BoundRegion
 }
 
-#[deriving(Clone, Eq, TotalEq, TotalOrd, Hash, Encodable, Decodable, ToStr, Show)]
+#[deriving(Clone, Eq, TotalEq, TotalOrd, Hash, Encodable, Decodable, Show)]
 pub enum BoundRegion {
     /// An anonymous region parameter for a given fn (&T)
     BrAnon(uint),
@@ -768,7 +771,7 @@ pub enum IntVarValue {
     UintType(ast::UintTy),
 }
 
-#[deriving(Clone, ToStr)]
+#[deriving(Clone, Show)]
 pub enum terr_vstore_kind {
     terr_vec,
     terr_str,
@@ -776,14 +779,14 @@ pub enum terr_vstore_kind {
     terr_trait
 }
 
-#[deriving(Clone, ToStr)]
+#[deriving(Clone, Show)]
 pub struct expected_found<T> {
     expected: T,
     found: T
 }
 
 // Data structures used in type unification
-#[deriving(Clone, ToStr)]
+#[deriving(Clone, Show)]
 pub enum type_err {
     terr_mismatch,
     terr_purity_mismatch(expected_found<Purity>),
@@ -826,7 +829,7 @@ pub struct ParamBounds {
 
 pub type BuiltinBounds = EnumSet<BuiltinBound>;
 
-#[deriving(Clone, Encodable, Eq, Decodable, Hash, ToStr)]
+#[deriving(Clone, Encodable, Eq, Decodable, Hash, Show)]
 #[repr(uint)]
 pub enum BuiltinBound {
     BoundStatic,
@@ -867,7 +870,7 @@ pub struct IntVid(uint);
 #[deriving(Clone, Eq, Hash)]
 pub struct FloatVid(uint);
 
-#[deriving(Clone, Eq, Encodable, Decodable, Hash, Show)]
+#[deriving(Clone, Eq, Encodable, Decodable, Hash)]
 pub struct RegionVid {
     id: uint
 }
@@ -879,7 +882,7 @@ pub enum InferTy {
     FloatVar(FloatVid)
 }
 
-#[deriving(Clone, Encodable, Decodable, Hash, ToStr, Show)]
+#[deriving(Clone, Encodable, Decodable, Hash, Show)]
 pub enum InferRegion {
     ReVar(RegionVid),
     ReSkolemized(uint, BoundRegion)
@@ -910,56 +913,64 @@ impl Vid for TyVid {
     fn to_uint(&self) -> uint { let TyVid(v) = *self; v }
 }
 
-impl ToStr for TyVid {
-    fn to_str(&self) -> ~str { format!("<generic \\#{}>", self.to_uint()) }
+impl fmt::Show for TyVid {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result{
+        write!(f.buf, "<generic \\#{}>", self.to_uint())
+    }
 }
 
 impl Vid for IntVid {
     fn to_uint(&self) -> uint { let IntVid(v) = *self; v }
 }
 
-impl ToStr for IntVid {
-    fn to_str(&self) -> ~str { format!("<generic integer \\#{}>", self.to_uint()) }
+impl fmt::Show for IntVid {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f.buf, "<generic integer \\#{}>", self.to_uint())
+    }
 }
 
 impl Vid for FloatVid {
     fn to_uint(&self) -> uint { let FloatVid(v) = *self; v }
 }
 
-impl ToStr for FloatVid {
-    fn to_str(&self) -> ~str { format!("<generic float \\#{}>", self.to_uint()) }
+impl fmt::Show for FloatVid {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f.buf, "<generic float \\#{}>", self.to_uint())
+    }
 }
 
 impl Vid for RegionVid {
     fn to_uint(&self) -> uint { self.id }
 }
 
-impl ToStr for RegionVid {
-    fn to_str(&self) -> ~str { format!("{:?}", self.id) }
-}
-
-impl ToStr for FnSig {
-    fn to_str(&self) -> ~str {
-        // grr, without tcx not much we can do.
-        return ~"(...)";
+impl fmt::Show for RegionVid {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        self.id.fmt(f)
     }
 }
 
-impl ToStr for InferTy {
-    fn to_str(&self) -> ~str {
+impl fmt::Show for FnSig {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        // grr, without tcx not much we can do.
+        write!(f.buf, "(...)")
+    }
+}
+
+impl fmt::Show for InferTy {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match *self {
-            TyVar(ref v) => v.to_str(),
-            IntVar(ref v) => v.to_str(),
-            FloatVar(ref v) => v.to_str()
+            TyVar(ref v) => v.fmt(f),
+            IntVar(ref v) => v.fmt(f),
+            FloatVar(ref v) => v.fmt(f),
         }
     }
 }
 
-impl ToStr for IntVarValue {
-    fn to_str(&self) -> ~str {
+impl fmt::Show for IntVarValue {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match *self {
-            IntType(ref v) => v.to_str(),
-            UintType(ref v) => v.to_str(),
+            IntType(ref v) => v.fmt(f),
+            UintType(ref v) => v.fmt(f),
         }
     }
 }
@@ -2020,9 +2031,9 @@ impl ops::Sub<TypeContents,TypeContents> for TypeContents {
     }
 }
 
-impl ToStr for TypeContents {
-    fn to_str(&self) -> ~str {
-        format!("TypeContents({:t})", self.bits)
+impl fmt::Show for TypeContents {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f.buf, "TypeContents({:t})", self.bits)
     }
 }
 
diff --git a/src/librustc/middle/typeck/variance.rs b/src/librustc/middle/typeck/variance.rs
index 47c40514e6c..bd244b431c2 100644
--- a/src/librustc/middle/typeck/variance.rs
+++ b/src/librustc/middle/typeck/variance.rs
@@ -197,6 +197,7 @@ use arena;
 use arena::Arena;
 use middle::ty;
 use std::vec;
+use std::fmt;
 use syntax::ast;
 use syntax::ast_util;
 use syntax::opt_vec;
@@ -235,13 +236,12 @@ enum VarianceTerm<'a> {
     InferredTerm(InferredIndex),
 }
 
-impl<'a> ToStr for VarianceTerm<'a> {
-    fn to_str(&self) -> ~str {
+impl<'a> fmt::Show for VarianceTerm<'a> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match *self {
-            ConstantTerm(c1) => format!("{}", c1.to_str()),
-            TransformTerm(v1, v2) => format!("({} \u00D7 {})",
-                                          v1.to_str(), v2.to_str()),
-            InferredTerm(id) => format!("[{}]", { let InferredIndex(i) = id; i })
+            ConstantTerm(c1) => write!(f.buf, "{}", c1),
+            TransformTerm(v1, v2) => write!(f.buf, "({} \u00D7 {})", v1, v2),
+            InferredTerm(id) => write!(f.buf, "[{}]", { let InferredIndex(i) = id; i })
         }
     }
 }
diff --git a/src/librustdoc/clean.rs b/src/librustdoc/clean.rs
index 6e6276e0457..2f6f6726be6 100644
--- a/src/librustdoc/clean.rs
+++ b/src/librustdoc/clean.rs
@@ -976,7 +976,7 @@ impl Clean<Item> for doctree::Static {
     }
 }
 
-#[deriving(ToStr, Clone, Encodable, Decodable)]
+#[deriving(Show, Clone, Encodable, Decodable)]
 pub enum Mutability {
     Mutable,
     Immutable,
diff --git a/src/librustdoc/doctree.rs b/src/librustdoc/doctree.rs
index 03186c16733..af082544532 100644
--- a/src/librustdoc/doctree.rs
+++ b/src/librustdoc/doctree.rs
@@ -58,7 +58,7 @@ impl Module {
     }
 }
 
-#[deriving(ToStr, Clone, Encodable, Decodable)]
+#[deriving(Show, Clone, Encodable, Decodable)]
 pub enum StructType {
     /// A normal struct
     Plain,
diff --git a/src/librustuv/lib.rs b/src/librustuv/lib.rs
index adbe4491886..9b327dc4ee4 100644
--- a/src/librustuv/lib.rs
+++ b/src/librustuv/lib.rs
@@ -45,8 +45,9 @@ via `close` and `delete` methods.
 #[cfg(test)] extern crate green;
 
 use std::cast;
-use std::io;
+use std::fmt;
 use std::io::IoError;
+use std::io;
 use std::libc::{c_int, c_void};
 use std::ptr::null;
 use std::ptr;
@@ -339,9 +340,9 @@ impl UvError {
     }
 }
 
-impl ToStr for UvError {
-    fn to_str(&self) -> ~str {
-        format!("{}: {}", self.name(), self.desc())
+impl fmt::Show for UvError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f.buf, "{}: {}", self.name(), self.desc())
     }
 }
 
diff --git a/src/libsemver/lib.rs b/src/libsemver/lib.rs
index d03d230d8bf..4c596b11ad6 100644
--- a/src/libsemver/lib.rs
+++ b/src/libsemver/lib.rs
@@ -38,7 +38,6 @@ use std::cmp;
 use std::fmt;
 use std::fmt::Show;
 use std::option::{Option, Some, None};
-use std::to_str::ToStr;
 
 /// An identifier in the pre-release or build metadata. If the identifier can
 /// be parsed as a decimal value, it will be represented with `Numeric`.
@@ -71,13 +70,6 @@ impl fmt::Show for Identifier {
     }
 }
 
-impl ToStr for Identifier {
-    #[inline]
-    fn to_str(&self) -> ~str {
-        format!("{}", *self)
-    }
-}
-
 
 /// Represents a version number conforming to the semantic versioning scheme.
 #[deriving(Clone, Eq)]
@@ -118,13 +110,6 @@ impl fmt::Show for Version {
     }
 }
 
-impl ToStr for Version {
-    #[inline]
-    fn to_str(&self) -> ~str {
-        format!("{}", *self)
-    }
-}
-
 impl cmp::Ord for Version {
     #[inline]
     fn lt(&self, other: &Version) -> bool {
diff --git a/src/libserialize/base64.rs b/src/libserialize/base64.rs
index 839450ce57c..f43c62f6ffc 100644
--- a/src/libserialize/base64.rs
+++ b/src/libserialize/base64.rs
@@ -10,6 +10,7 @@
 
 //! Base64 binary-to-text encoding
 use std::str;
+use std::fmt;
 
 /// Available encoding character sets
 pub enum CharacterSet {
@@ -165,12 +166,12 @@ pub enum FromBase64Error {
     InvalidBase64Length,
 }
 
-impl ToStr for FromBase64Error {
-    fn to_str(&self) -> ~str {
+impl fmt::Show for FromBase64Error {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match *self {
             InvalidBase64Character(ch, idx) =>
-                format!("Invalid character '{}' at position {}", ch, idx),
-            InvalidBase64Length => ~"Invalid length",
+                write!(f.buf, "Invalid character '{}' at position {}", ch, idx),
+            InvalidBase64Length => write!(f.buf, "Invalid length"),
         }
     }
 }
diff --git a/src/libserialize/hex.rs b/src/libserialize/hex.rs
index 223a586a5a0..5ec70773c3f 100644
--- a/src/libserialize/hex.rs
+++ b/src/libserialize/hex.rs
@@ -11,6 +11,7 @@
 //! Hex binary-to-text encoding
 use std::str;
 use std::vec;
+use std::fmt;
 
 /// A trait for converting a value to hexadecimal encoding
 pub trait ToHex {
@@ -65,12 +66,12 @@ pub enum FromHexError {
     InvalidHexLength,
 }
 
-impl ToStr for FromHexError {
-    fn to_str(&self) -> ~str {
+impl fmt::Show for FromHexError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match *self {
             InvalidHexCharacter(ch, idx) =>
-                format!("Invalid character '{}' at position {}", ch, idx),
-            InvalidHexLength => ~"Invalid input length",
+                write!(f.buf, "Invalid character '{}' at position {}", ch, idx),
+            InvalidHexLength => write!(f.buf, "Invalid input length"),
         }
     }
 }
diff --git a/src/libstd/any.rs b/src/libstd/any.rs
index 06ae20d60bc..551a34fc87f 100644
--- a/src/libstd/any.rs
+++ b/src/libstd/any.rs
@@ -24,7 +24,6 @@ use cast::transmute;
 use fmt;
 use option::{Option, Some, None};
 use result::{Result, Ok, Err};
-use to_str::ToStr;
 use intrinsics::TypeId;
 use intrinsics;
 
@@ -151,14 +150,6 @@ impl AnyOwnExt for ~Any {
 // Trait implementations
 ///////////////////////////////////////////////////////////////////////////////
 
-impl ToStr for ~Any {
-    fn to_str(&self) -> ~str { ~"~Any" }
-}
-
-impl<'a> ToStr for &'a Any {
-    fn to_str(&self) -> ~str { ~"&Any" }
-}
-
 impl fmt::Show for ~Any {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.pad("~Any")
diff --git a/src/libstd/ascii.rs b/src/libstd/ascii.rs
index 1ae36ab46aa..ac24a02c15b 100644
--- a/src/libstd/ascii.rs
+++ b/src/libstd/ascii.rs
@@ -10,7 +10,7 @@
 
 //! Operations on ASCII strings and characters
 
-use to_str::{ToStr, IntoStr};
+use to_str::{IntoStr};
 use str;
 use str::Str;
 use str::StrSlice;
@@ -127,14 +127,6 @@ impl Ascii {
     }
 }
 
-impl ToStr for Ascii {
-    #[inline]
-    fn to_str(&self) -> ~str {
-        // self.chr is always a valid utf8 byte, no need for the check
-        unsafe { str::raw::from_byte(self.chr) }
-    }
-}
-
 impl<'a> fmt::Show for Ascii {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         (self.chr as char).fmt(f)
diff --git a/src/libstd/bool.rs b/src/libstd/bool.rs
index af745f94fb5..918d42e1bce 100644
--- a/src/libstd/bool.rs
+++ b/src/libstd/bool.rs
@@ -17,7 +17,6 @@
 //! Implementations of the following traits:
 //!
 //! * `FromStr`
-//! * `ToStr`
 //! * `Not`
 //! * `Ord`
 //! * `TotalOrd`
@@ -34,7 +33,6 @@
 
 use option::{None, Option, Some};
 use from_str::FromStr;
-use to_str::ToStr;
 use num::FromPrimitive;
 
 #[cfg(not(test))] use cmp::{Eq, Ord, TotalOrd, Ordering};
@@ -179,21 +177,6 @@ impl FromStr for bool {
     }
 }
 
-impl ToStr for bool {
-    /// Convert a `bool` to a string.
-    ///
-    /// # Examples
-    ///
-    /// ```rust
-    /// assert_eq!(true.to_str(), ~"true");
-    /// assert_eq!(false.to_str(), ~"false");
-    /// ```
-    #[inline]
-    fn to_str(&self) -> ~str {
-        if *self { ~"true" } else { ~"false" }
-    }
-}
-
 #[cfg(not(test))]
 impl Not<bool> for bool {
     /// The logical complement of a boolean value.
diff --git a/src/libstd/char.rs b/src/libstd/char.rs
index 1ec89d1850f..ed2a88e644b 100644
--- a/src/libstd/char.rs
+++ b/src/libstd/char.rs
@@ -15,8 +15,6 @@ use option::{None, Option, Some};
 use iter::{Iterator, range_step};
 use str::StrSlice;
 use unicode::{derived_property, property, general_category, decompose};
-use to_str::ToStr;
-use str;
 
 #[cfg(test)] use str::OwnedStr;
 
@@ -344,13 +342,6 @@ pub fn len_utf8_bytes(c: char) -> uint {
     }
 }
 
-impl ToStr for char {
-    #[inline]
-    fn to_str(&self) -> ~str {
-        str::from_char(*self)
-    }
-}
-
 #[allow(missing_doc)]
 pub trait Char {
     fn is_alphabetic(&self) -> bool;
@@ -556,6 +547,7 @@ fn test_escape_unicode() {
 
 #[test]
 fn test_to_str() {
+    use to_str::ToStr;
     let s = 't'.to_str();
     assert_eq!(s, ~"t");
 }
diff --git a/src/libstd/fmt/mod.rs b/src/libstd/fmt/mod.rs
index a55794b08fe..5c0838fadca 100644
--- a/src/libstd/fmt/mod.rs
+++ b/src/libstd/fmt/mod.rs
@@ -1055,6 +1055,16 @@ pub fn argumentuint<'a>(s: &'a uint) -> Argument<'a> {
 
 // Implementations of the core formatting traits
 
+impl<T: Show> Show for @T {
+    fn fmt(&self, f: &mut Formatter) -> Result { secret_show(&**self, f) }
+}
+impl<T: Show> Show for ~T {
+    fn fmt(&self, f: &mut Formatter) -> Result { secret_show(&**self, f) }
+}
+impl<'a, T: Show> Show for &'a T {
+    fn fmt(&self, f: &mut Formatter) -> Result { secret_show(*self, f) }
+}
+
 impl Bool for bool {
     fn fmt(&self, f: &mut Formatter) -> Result {
         secret_string(&(if *self {"true"} else {"false"}), f)
diff --git a/src/libstd/io/mod.rs b/src/libstd/io/mod.rs
index 91a8d599326..94d32d6d8f3 100644
--- a/src/libstd/io/mod.rs
+++ b/src/libstd/io/mod.rs
@@ -188,7 +188,6 @@ use path::Path;
 use result::{Ok, Err, Result};
 use str::{StrSlice, OwnedStr};
 use str;
-use to_str::ToStr;
 use uint;
 use unstable::finally::try_finally;
 use vec::{OwnedVector, MutableVector, ImmutableVector, OwnedCloneableVector};
@@ -286,21 +285,7 @@ impl fmt::Show for IoError {
     }
 }
 
-// FIXME: #8242 implementing manually because deriving doesn't work for some reason
-impl ToStr for IoError {
-    fn to_str(&self) -> ~str {
-        let mut s = ~"IoError { kind: ";
-        s.push_str(self.kind.to_str());
-        s.push_str(", desc: ");
-        s.push_str(self.desc);
-        s.push_str(", detail: ");
-        s.push_str(self.detail.to_str());
-        s.push_str(" }");
-        s
-    }
-}
-
-#[deriving(Eq, Clone)]
+#[deriving(Eq, Clone, Show)]
 pub enum IoErrorKind {
     OtherIoError,
     EndOfFile,
@@ -321,31 +306,6 @@ pub enum IoErrorKind {
     InvalidInput,
 }
 
-// FIXME: #8242 implementing manually because deriving doesn't work for some reason
-impl ToStr for IoErrorKind {
-    fn to_str(&self) -> ~str {
-        match *self {
-            OtherIoError => ~"OtherIoError",
-            EndOfFile => ~"EndOfFile",
-            FileNotFound => ~"FileNotFound",
-            PermissionDenied => ~"PermissionDenied",
-            ConnectionFailed => ~"ConnectionFailed",
-            Closed => ~"Closed",
-            ConnectionRefused => ~"ConnectionRefused",
-            ConnectionReset => ~"ConnectionReset",
-            NotConnected => ~"NotConnected",
-            BrokenPipe => ~"BrokenPipe",
-            PathAlreadyExists => ~"PathAlreadyExists",
-            PathDoesntExist => ~"PathDoesntExist",
-            MismatchedFileTypeForOperation => ~"MismatchedFileTypeForOperation",
-            IoUnavailable => ~"IoUnavailable",
-            ResourceUnavailable => ~"ResourceUnavailable",
-            ConnectionAborted => ~"ConnectionAborted",
-            InvalidInput => ~"InvalidInput",
-        }
-    }
-}
-
 pub trait Reader {
 
     // Only method which need to get implemented for this trait
diff --git a/src/libstd/io/net/ip.rs b/src/libstd/io/net/ip.rs
index 13ea552ab3b..e4f36764323 100644
--- a/src/libstd/io/net/ip.rs
+++ b/src/libstd/io/net/ip.rs
@@ -9,11 +9,11 @@
 // except according to those terms.
 
 use container::Container;
+use fmt;
 use from_str::FromStr;
 use iter::Iterator;
 use option::{Option, None, Some};
 use str::StrSlice;
-use to_str::ToStr;
 use vec::{MutableCloneableVector, ImmutableVector, MutableVector};
 
 pub type Port = u16;
@@ -24,26 +24,27 @@ pub enum IpAddr {
     Ipv6Addr(u16, u16, u16, u16, u16, u16, u16, u16)
 }
 
-impl ToStr for IpAddr {
-    fn to_str(&self) -> ~str {
+impl fmt::Show for IpAddr {
+    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
         match *self {
             Ipv4Addr(a, b, c, d) =>
-                format!("{}.{}.{}.{}", a, b, c, d),
+                write!(fmt.buf, "{}.{}.{}.{}", a, b, c, d),
 
             // Ipv4 Compatible address
             Ipv6Addr(0, 0, 0, 0, 0, 0, g, h) => {
-                format!("::{}.{}.{}.{}", (g >> 8) as u8, g as u8,
-                        (h >> 8) as u8, h as u8)
+                write!(fmt.buf, "::{}.{}.{}.{}", (g >> 8) as u8, g as u8,
+                       (h >> 8) as u8, h as u8)
             }
 
             // Ipv4-Mapped address
             Ipv6Addr(0, 0, 0, 0, 0, 0xFFFF, g, h) => {
-                format!("::FFFF:{}.{}.{}.{}", (g >> 8) as u8, g as u8,
-                        (h >> 8) as u8, h as u8)
+                write!(fmt.buf, "::FFFF:{}.{}.{}.{}", (g >> 8) as u8, g as u8,
+                       (h >> 8) as u8, h as u8)
             }
 
             Ipv6Addr(a, b, c, d, e, f, g, h) =>
-                format!("{:x}:{:x}:{:x}:{:x}:{:x}:{:x}:{:x}:{:x}", a, b, c, d, e, f, g, h)
+                write!(fmt.buf, "{:x}:{:x}:{:x}:{:x}:{:x}:{:x}:{:x}:{:x}",
+                       a, b, c, d, e, f, g, h)
         }
     }
 }
@@ -55,11 +56,11 @@ pub struct SocketAddr {
 }
 
 
-impl ToStr for SocketAddr {
-    fn to_str(&self) -> ~str {
+impl fmt::Show for SocketAddr {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match self.ip {
-            Ipv4Addr(..) => format!("{}:{}", self.ip.to_str(), self.port),
-            Ipv6Addr(..) => format!("[{}]:{}", self.ip.to_str(), self.port),
+            Ipv4Addr(..) => write!(f.buf, "{}:{}", self.ip, self.port),
+            Ipv6Addr(..) => write!(f.buf, "[{}]:{}", self.ip, self.port),
         }
     }
 }
diff --git a/src/libstd/num/f32.rs b/src/libstd/num/f32.rs
index 7b1fe949199..a4eac564ee6 100644
--- a/src/libstd/num/f32.rs
+++ b/src/libstd/num/f32.rs
@@ -19,7 +19,6 @@ use libc::{c_float, c_int};
 use num::{FPCategory, FPNaN, FPInfinite , FPZero, FPSubnormal, FPNormal};
 use num::{Zero, One, Bounded, strconv};
 use num;
-use to_str;
 use intrinsics;
 
 macro_rules! delegate(
@@ -745,11 +744,6 @@ pub fn to_str_exp_digits(num: f32, dig: uint, upper: bool) -> ~str {
     r
 }
 
-impl to_str::ToStr for f32 {
-    #[inline]
-    fn to_str(&self) -> ~str { to_str_digits(*self, 8) }
-}
-
 impl num::ToStrRadix for f32 {
     /// Converts a float to a string in a given radix
     ///
diff --git a/src/libstd/num/f64.rs b/src/libstd/num/f64.rs
index d5a571cdd23..e6b903cbbdb 100644
--- a/src/libstd/num/f64.rs
+++ b/src/libstd/num/f64.rs
@@ -20,7 +20,6 @@ use libc::{c_double, c_int};
 use num::{FPCategory, FPNaN, FPInfinite , FPZero, FPSubnormal, FPNormal};
 use num::{Zero, One, Bounded, strconv};
 use num;
-use to_str;
 use intrinsics;
 
 pub use cmp::{min, max};
@@ -747,11 +746,6 @@ pub fn to_str_exp_digits(num: f64, dig: uint, upper: bool) -> ~str {
     r
 }
 
-impl to_str::ToStr for f64 {
-    #[inline]
-    fn to_str(&self) -> ~str { to_str_digits(*self, 8) }
-}
-
 impl num::ToStrRadix for f64 {
     /// Converts a float to a string in a given radix
     ///
diff --git a/src/libstd/num/int_macros.rs b/src/libstd/num/int_macros.rs
index 43a70190812..030aa2d81fa 100644
--- a/src/libstd/num/int_macros.rs
+++ b/src/libstd/num/int_macros.rs
@@ -273,14 +273,6 @@ pub fn to_str_bytes<U>(n: $T, radix: uint, f: |v: &[u8]| -> U) -> U {
     f(buf.slice(0, cur))
 }
 
-impl ToStr for $T {
-    /// Convert to a string in base 10.
-    #[inline]
-    fn to_str(&self) -> ~str {
-        format!("{:d}", *self)
-    }
-}
-
 impl ToStrRadix for $T {
     /// Convert to a string in a given base.
     #[inline]
diff --git a/src/libstd/num/uint_macros.rs b/src/libstd/num/uint_macros.rs
index d60b5235446..001927e6033 100644
--- a/src/libstd/num/uint_macros.rs
+++ b/src/libstd/num/uint_macros.rs
@@ -187,14 +187,6 @@ pub fn to_str_bytes<U>(n: $T, radix: uint, f: |v: &[u8]| -> U) -> U {
     f(buf.slice(0, cur))
 }
 
-impl ToStr for $T {
-    /// Convert to a string in base 10.
-    #[inline]
-    fn to_str(&self) -> ~str {
-        format!("{:u}", *self)
-    }
-}
-
 impl ToStrRadix for $T {
     /// Convert to a string in a given base.
     #[inline]
diff --git a/src/libstd/option.rs b/src/libstd/option.rs
index 44d78be93d6..633d6e92c70 100644
--- a/src/libstd/option.rs
+++ b/src/libstd/option.rs
@@ -42,16 +42,13 @@ use clone::Clone;
 use clone::DeepClone;
 use cmp::{Eq, TotalEq, TotalOrd};
 use default::Default;
-use fmt;
 use iter::{Iterator, DoubleEndedIterator, FromIterator, ExactSize};
 use kinds::Send;
 use mem;
-use str::OwnedStr;
-use to_str::ToStr;
 use vec;
 
 /// The option type
-#[deriving(Clone, DeepClone, Eq, Ord, TotalEq, TotalOrd, ToStr)]
+#[deriving(Clone, DeepClone, Eq, Ord, TotalEq, TotalOrd, Show)]
 pub enum Option<T> {
     /// No value
     None,
@@ -380,16 +377,6 @@ impl<T: Default> Option<T> {
 // Trait implementations
 /////////////////////////////////////////////////////////////////////////////
 
-impl<T: fmt::Show> fmt::Show for Option<T> {
-    #[inline]
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        match *self {
-            Some(ref t) => write!(f.buf, "Some({})", *t),
-            None        => write!(f.buf, "None")
-        }
-    }
-}
-
 impl<T> Default for Option<T> {
     #[inline]
     fn default() -> Option<T> { None }
diff --git a/src/libstd/path/mod.rs b/src/libstd/path/mod.rs
index 13496033fd0..09124f63361 100644
--- a/src/libstd/path/mod.rs
+++ b/src/libstd/path/mod.rs
@@ -71,7 +71,6 @@ use iter::Iterator;
 use option::{Option, None, Some};
 use str;
 use str::{MaybeOwned, OwnedStr, Str, StrSlice, from_utf8_lossy};
-use to_str::ToStr;
 use vec;
 use vec::{CloneableVector, OwnedCloneableVector, OwnedVector, Vector};
 use vec::{ImmutableEqVector, ImmutableVector};
@@ -499,16 +498,6 @@ impl<'a, P: GenericPath> fmt::Show for Display<'a, P> {
     }
 }
 
-impl<'a, P: GenericPath> ToStr for Display<'a, P> {
-    /// Returns the path as a string
-    ///
-    /// If the path is not UTF-8, invalid sequences with be replaced with the
-    /// unicode replacement char. This involves allocation.
-    fn to_str(&self) -> ~str {
-        self.as_maybe_owned().into_owned()
-    }
-}
-
 impl<'a, P: GenericPath> Display<'a, P> {
     /// Returns the path as a possibly-owned string.
     ///
diff --git a/src/libstd/result.rs b/src/libstd/result.rs
index 39e8b6ad6c1..3f09351ead6 100644
--- a/src/libstd/result.rs
+++ b/src/libstd/result.rs
@@ -12,14 +12,11 @@
 
 use clone::Clone;
 use cmp::Eq;
-use fmt;
 use iter::{Iterator, FromIterator};
 use option::{None, Option, Some};
-use str::OwnedStr;
-use to_str::ToStr;
 
 /// `Result` is a type that represents either success (`Ok`) or failure (`Err`).
-#[deriving(Clone, DeepClone, Eq, Ord, TotalEq, TotalOrd, ToStr)]
+#[deriving(Clone, DeepClone, Eq, Ord, TotalEq, TotalOrd, Show)]
 #[must_use]
 pub enum Result<T, E> {
     /// Contains the success value
@@ -202,20 +199,6 @@ impl<T, E> Result<T, E> {
     }
 }
 
-/////////////////////////////////////////////////////////////////////////////
-// Trait implementations
-/////////////////////////////////////////////////////////////////////////////
-
-impl<T: fmt::Show, E: fmt::Show> fmt::Show for Result<T, E> {
-    #[inline]
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        match *self {
-            Ok(ref t) => write!(f.buf, "Ok({})", *t),
-            Err(ref e) => write!(f.buf, "Err({})", *e)
-        }
-    }
-}
-
 /////////////////////////////////////////////////////////////////////////////
 // Free functions
 /////////////////////////////////////////////////////////////////////////////
diff --git a/src/libstd/str.rs b/src/libstd/str.rs
index 3c094cd631d..daaf46be187 100644
--- a/src/libstd/str.rs
+++ b/src/libstd/str.rs
@@ -98,7 +98,6 @@ use num::Saturating;
 use option::{None, Option, Some};
 use ptr;
 use ptr::RawPtr;
-use to_str::ToStr;
 use from_str::FromStr;
 use vec;
 use vec::{OwnedVector, OwnedCloneableVector, ImmutableVector, MutableVector};
@@ -132,21 +131,11 @@ pub fn from_utf8<'a>(v: &'a [u8]) -> Option<&'a str> {
     } else { None }
 }
 
-impl ToStr for ~str {
-    #[inline]
-    fn to_str(&self) -> ~str { self.to_owned() }
-}
-
 impl FromStr for ~str {
     #[inline]
     fn from_str(s: &str) -> Option<~str> { Some(s.to_owned()) }
 }
 
-impl<'a> ToStr for &'a str {
-    #[inline]
-    fn to_str(&self) -> ~str { self.to_owned() }
-}
-
 /// Convert a byte to a UTF-8 string
 ///
 /// # Failure
@@ -1269,11 +1258,6 @@ impl<'a> IntoMaybeOwned<'a> for MaybeOwned<'a> {
     fn into_maybe_owned(self) -> MaybeOwned<'a> { self }
 }
 
-impl<'a> ToStr for MaybeOwned<'a> {
-    #[inline]
-    fn to_str(&self) -> ~str { self.as_slice().to_owned() }
-}
-
 impl<'a> Eq for MaybeOwned<'a> {
     #[inline]
     fn eq(&self, other: &MaybeOwned) -> bool {
diff --git a/src/libstd/to_str.rs b/src/libstd/to_str.rs
index 46a9e93f416..ba3c1c0fc45 100644
--- a/src/libstd/to_str.rs
+++ b/src/libstd/to_str.rs
@@ -14,10 +14,7 @@ The `ToStr` trait for converting to strings
 
 */
 
-use option::{Some, None};
-use str::OwnedStr;
-use iter::Iterator;
-use vec::ImmutableVector;
+use fmt;
 
 /// A generic trait for converting a value to a string
 pub trait ToStr {
@@ -31,47 +28,8 @@ pub trait IntoStr {
     fn into_str(self) -> ~str;
 }
 
-impl ToStr for () {
-    #[inline]
-    fn to_str(&self) -> ~str { ~"()" }
-}
-
-impl<'a,A:ToStr> ToStr for &'a [A] {
-    #[inline]
-    fn to_str(&self) -> ~str {
-        let mut acc = ~"[";
-        let mut first = true;
-        for elt in self.iter() {
-            if first {
-                first = false;
-            }
-            else {
-                acc.push_str(", ");
-            }
-            acc.push_str(elt.to_str());
-        }
-        acc.push_char(']');
-        acc
-    }
-}
-
-impl<A:ToStr> ToStr for ~[A] {
-    #[inline]
-    fn to_str(&self) -> ~str {
-        let mut acc = ~"[";
-        let mut first = true;
-        for elt in self.iter() {
-            if first {
-                first = false;
-            }
-            else {
-                acc.push_str(", ");
-            }
-            acc.push_str(elt.to_str());
-        }
-        acc.push_char(']');
-        acc
-    }
+impl<T: fmt::Show> ToStr for T {
+    fn to_str(&self) -> ~str { format!("{}", *self) }
 }
 
 #[cfg(test)]
diff --git a/src/libstd/tuple.rs b/src/libstd/tuple.rs
index b0d51cba103..9d50337efab 100644
--- a/src/libstd/tuple.rs
+++ b/src/libstd/tuple.rs
@@ -17,7 +17,6 @@ use clone::Clone;
 #[cfg(not(test))] use default::Default;
 use fmt;
 use result::{Ok, Err};
-use to_str::ToStr;
 
 // macro for implementing n-ary tuple functions and operations
 macro_rules! tuple_impls {
@@ -119,12 +118,6 @@ macro_rules! tuple_impls {
                 }
             }
 
-            impl<$($T: fmt::Show),+> ToStr for ($($T,)+) {
-                fn to_str(&self) -> ~str {
-                    format!("{}", *self)
-                }
-            }
-
             impl<$($T: fmt::Show),+> fmt::Show for ($($T,)+) {
                 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
                     write_tuple!(f.buf, $(self.$refN()),+)
diff --git a/src/libsyntax/abi.rs b/src/libsyntax/abi.rs
index 13725ef2473..faf24da74cc 100644
--- a/src/libsyntax/abi.rs
+++ b/src/libsyntax/abi.rs
@@ -9,6 +9,8 @@
 // except according to those terms.
 
 use std::hash::{Hash, sip};
+use std::fmt;
+use std::fmt::Show;
 
 #[deriving(Eq)]
 pub enum Os { OsWin32, OsMacos, OsLinux, OsAndroid, OsFreebsd, }
@@ -271,20 +273,23 @@ impl Hash for Abi {
     }
 }
 
-impl ToStr for Abi {
-    fn to_str(&self) -> ~str {
-        self.data().name.to_str()
+impl fmt::Show for Abi {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        self.data().name.fmt(f)
     }
 }
 
-impl ToStr for AbiSet {
-    fn to_str(&self) -> ~str {
-        let mut strs = ~[];
+impl fmt::Show for AbiSet {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        if_ok!(write!(f.buf, "\""));
+        let mut first = true;
         self.each(|abi| {
-            strs.push(abi.data().name);
+            if first { first = false; }
+            else { let _ = write!(f.buf, " "); }
+            let _ = write!(f.buf, "{}", abi.data().name);
             true
         });
-        format!("\"{}\"", strs.connect(" "))
+        write!(f.buf, "\"")
     }
 }
 
diff --git a/src/libsyntax/ast.rs b/src/libsyntax/ast.rs
index 4e43592ec5c..7561d8cbbae 100644
--- a/src/libsyntax/ast.rs
+++ b/src/libsyntax/ast.rs
@@ -17,11 +17,12 @@ use opt_vec::OptVec;
 use parse::token::{InternedString, special_idents, str_to_ident};
 use parse::token;
 
+use std::fmt;
+use std::fmt::Show;
 use std::cell::RefCell;
 use collections::HashMap;
 use std::option::Option;
 use std::rc::Rc;
-use std::to_str::ToStr;
 use serialize::{Encodable, Decodable, Encoder, Decoder};
 
 /// A pointer abstraction. FIXME(eddyb) #10676 use Rc<T> in the future.
@@ -39,7 +40,7 @@ pub fn P<T: 'static>(value: T) -> P<T> {
 // table) and a SyntaxContext to track renaming and
 // macro expansion per Flatt et al., "Macros
 // That Work Together"
-#[deriving(Clone, Hash, ToStr, TotalEq, TotalOrd, Show)]
+#[deriving(Clone, Hash, TotalEq, TotalOrd, Show)]
 pub struct Ident { name: Name, ctxt: SyntaxContext }
 
 impl Ident {
@@ -182,7 +183,7 @@ pub type CrateNum = u32;
 
 pub type NodeId = u32;
 
-#[deriving(Clone, TotalEq, TotalOrd, Eq, Encodable, Decodable, Hash, ToStr, Show)]
+#[deriving(Clone, TotalEq, TotalOrd, Eq, Encodable, Decodable, Hash, Show)]
 pub struct DefId {
     krate: CrateNum,
     node: NodeId,
@@ -277,7 +278,7 @@ pub enum Def {
     DefMethod(DefId /* method */, Option<DefId> /* trait */),
 }
 
-#[deriving(Clone, Eq, Hash, Encodable, Decodable, ToStr)]
+#[deriving(Clone, Eq, Hash, Encodable, Decodable, Show)]
 pub enum DefRegion {
     DefStaticRegion,
     DefEarlyBoundRegion(/* index */ uint, /* lifetime decl */ NodeId),
@@ -398,12 +399,12 @@ pub enum Sigil {
     ManagedSigil
 }
 
-impl ToStr for Sigil {
-    fn to_str(&self) -> ~str {
+impl fmt::Show for Sigil {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match *self {
-            BorrowedSigil => ~"&",
-            OwnedSigil => ~"~",
-            ManagedSigil => ~"@"
+            BorrowedSigil => "&".fmt(f),
+            OwnedSigil => "~".fmt(f),
+            ManagedSigil => "@".fmt(f),
          }
     }
 }
@@ -768,9 +769,9 @@ pub enum IntTy {
     TyI64,
 }
 
-impl ToStr for IntTy {
-    fn to_str(&self) -> ~str {
-        ast_util::int_ty_to_str(*self)
+impl fmt::Show for IntTy {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f.buf, "{}", ast_util::int_ty_to_str(*self))
     }
 }
 
@@ -783,9 +784,9 @@ pub enum UintTy {
     TyU64,
 }
 
-impl ToStr for UintTy {
-    fn to_str(&self) -> ~str {
-        ast_util::uint_ty_to_str(*self)
+impl fmt::Show for UintTy {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f.buf, "{}", ast_util::uint_ty_to_str(*self))
     }
 }
 
@@ -795,9 +796,9 @@ pub enum FloatTy {
     TyF64,
 }
 
-impl ToStr for FloatTy {
-    fn to_str(&self) -> ~str {
-        ast_util::float_ty_to_str(*self)
+impl fmt::Show for FloatTy {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f.buf, "{}", ast_util::float_ty_to_str(*self))
     }
 }
 
@@ -826,11 +827,11 @@ pub enum Onceness {
     Many
 }
 
-impl ToStr for Onceness {
-    fn to_str(&self) -> ~str {
+impl fmt::Show for Onceness {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match *self {
-            Once => ~"once",
-            Many => ~"many"
+            Once => "once".fmt(f),
+            Many => "many".fmt(f),
         }
     }
 }
@@ -939,12 +940,12 @@ pub enum Purity {
     ExternFn, // declared with "extern fn"
 }
 
-impl ToStr for Purity {
-    fn to_str(&self) -> ~str {
+impl fmt::Show for Purity {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match *self {
-            ImpureFn => ~"impure",
-            UnsafeFn => ~"unsafe",
-            ExternFn => ~"extern"
+            ImpureFn => "impure".fmt(f),
+            UnsafeFn => "unsafe".fmt(f),
+            ExternFn => "extern".fmt(f),
         }
     }
 }
diff --git a/src/libsyntax/ast_map.rs b/src/libsyntax/ast_map.rs
index 26c4b07fc96..9194cfb0694 100644
--- a/src/libsyntax/ast_map.rs
+++ b/src/libsyntax/ast_map.rs
@@ -22,6 +22,7 @@ use std::logging;
 use std::cell::RefCell;
 use std::iter;
 use std::vec;
+use std::fmt;
 
 #[deriving(Clone, Eq)]
 pub enum PathElem {
@@ -37,9 +38,10 @@ impl PathElem {
     }
 }
 
-impl ToStr for PathElem {
-    fn to_str(&self) -> ~str {
-        token::get_name(self.name()).get().to_str()
+impl fmt::Show for PathElem {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        let slot = token::get_name(self.name());
+        write!(f.buf, "{}", slot.get())
     }
 }
 
diff --git a/src/libsyntax/attr.rs b/src/libsyntax/attr.rs
index 93edb552bbe..27d1c6fa649 100644
--- a/src/libsyntax/attr.rs
+++ b/src/libsyntax/attr.rs
@@ -341,7 +341,7 @@ pub struct Stability {
 }
 
 /// The available stability levels.
-#[deriving(Eq,Ord,Clone,ToStr)]
+#[deriving(Eq,Ord,Clone,Show)]
 pub enum StabilityLevel {
     Deprecated,
     Experimental,
diff --git a/src/libsyntax/crateid.rs b/src/libsyntax/crateid.rs
index 0831f319ce7..d04bedc65b5 100644
--- a/src/libsyntax/crateid.rs
+++ b/src/libsyntax/crateid.rs
@@ -8,6 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+use std::fmt;
+
 /// CrateIds identify crates and include the crate name and optionally a path
 /// and version. In the full form, they look like relative URLs. Example:
 /// `github.com/mozilla/rust#std:1.0` would be a package ID with a path of
@@ -26,16 +28,17 @@ pub struct CrateId {
     version: Option<~str>,
 }
 
-impl ToStr for CrateId {
-    fn to_str(&self) -> ~str {
+impl fmt::Show for CrateId {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        if_ok!(write!(f.buf, "{}", self.path));
         let version = match self.version {
             None => "0.0",
             Some(ref version) => version.as_slice(),
         };
         if self.path == self.name || self.path.ends_with(format!("/{}", self.name)) {
-            format!("{}\\#{}", self.path, version)
+            write!(f.buf, "\\#{}", version)
         } else {
-            format!("{}\\#{}:{}", self.path, self.name, version)
+            write!(f.buf, "\\#{}:{}", self.name, version)
         }
     }
 }
diff --git a/src/libsyntax/diagnostic.rs b/src/libsyntax/diagnostic.rs
index 8cf0f128d22..be45008b92a 100644
--- a/src/libsyntax/diagnostic.rs
+++ b/src/libsyntax/diagnostic.rs
@@ -12,8 +12,9 @@ use codemap::{Pos, Span};
 use codemap;
 
 use std::cell::Cell;
-use std::io;
+use std::fmt;
 use std::io::stdio::StdWriter;
+use std::io;
 use std::iter::range;
 use std::local_data;
 use term;
@@ -162,12 +163,14 @@ pub enum Level {
     Note,
 }
 
-impl ToStr for Level {
-    fn to_str(&self) -> ~str {
+impl fmt::Show for Level {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        use std::fmt::Show;
+
         match *self {
-            Fatal | Error => ~"error",
-            Warning => ~"warning",
-            Note => ~"note"
+            Fatal | Error => "error".fmt(f),
+            Warning => "warning".fmt(f),
+            Note => "note".fmt(f),
         }
     }
 }
diff --git a/src/libtest/lib.rs b/src/libtest/lib.rs
index c9bdd49f86c..a81fc4f6d69 100644
--- a/src/libtest/lib.rs
+++ b/src/libtest/lib.rs
@@ -40,14 +40,14 @@ use term::Terminal;
 use term::color::{Color, RED, YELLOW, GREEN, CYAN};
 
 use std::cmp;
-use std::io;
-use std::io::{File, PortReader, ChanWriter};
+use std::f64;
+use std::fmt;
 use std::io::stdio::StdWriter;
+use std::io::{File, PortReader, ChanWriter};
+use std::io;
+use std::os;
 use std::str;
 use std::task;
-use std::to_str::ToStr;
-use std::f64;
-use std::os;
 
 // to be used by rustc to compile tests in libtest
 pub mod test {
@@ -70,11 +70,11 @@ pub enum TestName {
     StaticTestName(&'static str),
     DynTestName(~str)
 }
-impl ToStr for TestName {
-    fn to_str(&self) -> ~str {
-        match (*self).clone() {
-            StaticTestName(s) => s.to_str(),
-            DynTestName(s) => s.to_str()
+impl fmt::Show for TestName {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match *self {
+            StaticTestName(s) => f.buf.write_str(s),
+            DynTestName(ref s) => f.buf.write_str(s.as_slice()),
         }
     }
 }
diff --git a/src/libuuid/lib.rs b/src/libuuid/lib.rs
index dec27719beb..7a078e4b571 100644
--- a/src/libuuid/lib.rs
+++ b/src/libuuid/lib.rs
@@ -64,17 +64,15 @@ Examples of string representations:
 extern crate test;
 extern crate serialize;
 
-use std::str;
-use std::vec;
-use std::num::FromStrRadix;
-use std::char::Char;
-use std::container::Container;
-use std::to_str::ToStr;
-use std::rand;
-use std::rand::Rng;
-use std::cmp::Eq;
 use std::cast::{transmute,transmute_copy};
+use std::cast::{transmute,transmute_copy};
+use std::char::Char;
+use std::cmp::Eq;
+use std::cmp::Eq;
+use std::fmt;
 use std::hash::{Hash, sip};
+use std::num::FromStrRadix;
+use std::rand::Rng;
 
 use serialize::{Encoder, Encodable, Decoder, Decodable};
 
@@ -142,22 +140,21 @@ pub enum ParseError {
 }
 
 /// Converts a ParseError to a string
-impl ToStr for ParseError {
-    #[inline]
-    fn to_str(&self) -> ~str {
+impl fmt::Show for ParseError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match *self {
             ErrorInvalidLength(found) =>
-                format!("Invalid length; expecting 32, 36 or 45 chars, found {}",
-                        found),
+                write!(f.buf, "Invalid length; expecting 32, 36 or 45 chars, \
+                               found {}", found),
             ErrorInvalidCharacter(found, pos) =>
-                format!("Invalid character; found `{}` (0x{:02x}) at offset {}",
-                        found, found as uint, pos),
+                write!(f.buf, "Invalid character; found `{}` (0x{:02x}) at \
+                               offset {}", found, found as uint, pos),
             ErrorInvalidGroups(found) =>
-                format!("Malformed; wrong number of groups: expected 1 or 5, found {}",
-                        found),
+                write!(f.buf, "Malformed; wrong number of groups: expected 1 \
+                               or 5, found {}", found),
             ErrorInvalidGroupLength(group, found, expecting) =>
-                format!("Malformed; length of group {} was {}, expecting {}",
-                        group, found, expecting),
+                write!(f.buf, "Malformed; length of group {} was {}, \
+                               expecting {}", group, found, expecting),
         }
     }
 }
@@ -465,9 +462,9 @@ impl FromStr for Uuid {
 }
 
 /// Convert the UUID to a hexadecimal-based string representation
-impl ToStr for Uuid {
-    fn to_str(&self) -> ~str {
-        self.to_simple_str()
+impl fmt::Show for Uuid {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f.buf, "{}", self.to_simple_str())
     }
 }
 
diff --git a/src/test/auxiliary/cci_class_cast.rs b/src/test/auxiliary/cci_class_cast.rs
index 8fac4a3f322..79bb5aef764 100644
--- a/src/test/auxiliary/cci_class_cast.rs
+++ b/src/test/auxiliary/cci_class_cast.rs
@@ -9,14 +9,18 @@
 // except according to those terms.
 
 pub mod kitty {
+    use std::fmt;
+
     pub struct cat {
       priv meows : uint,
       how_hungry : int,
       name : ~str,
     }
 
-    impl ToStr for cat {
-       fn to_str(&self) -> ~str { self.name.clone() }
+    impl fmt::Show for cat {
+        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+            write!(f.buf, "{}", self.name)
+        }
     }
 
     impl cat {
diff --git a/src/test/compile-fail/use-after-move-implicity-coerced-object.rs b/src/test/compile-fail/use-after-move-implicity-coerced-object.rs
index 537da535457..085ed5db6df 100644
--- a/src/test/compile-fail/use-after-move-implicity-coerced-object.rs
+++ b/src/test/compile-fail/use-after-move-implicity-coerced-object.rs
@@ -10,13 +10,15 @@
 
 // ignore-tidy-linelength
 
+use std::fmt;
+
 struct Number {
     n: i64
 }
 
-impl ToStr for Number {
-    fn to_str(&self) -> ~str {
-        self.n.to_str()
+impl fmt::Show for Number {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f.buf, "{}", self.n)
     }
 }
 
diff --git a/src/test/run-pass/class-separate-impl.rs b/src/test/run-pass/class-separate-impl.rs
index e813210f4f4..55fa783391a 100644
--- a/src/test/run-pass/class-separate-impl.rs
+++ b/src/test/run-pass/class-separate-impl.rs
@@ -9,6 +9,9 @@
 // except according to those terms.
 
 // ignore-fast
+
+use std::fmt;
+
 struct cat {
     meows : uint,
 
@@ -50,9 +53,9 @@ fn cat(in_x : uint, in_y : int, in_name: ~str) -> cat {
     }
 }
 
-impl ToStr for cat {
-    fn to_str(&self) -> ~str {
-        self.name.clone()
+impl fmt::Show for cat {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f.buf, "{}", self.name)
     }
 }
 
diff --git a/src/test/run-pass/deriving-global.rs b/src/test/run-pass/deriving-global.rs
index ffca06dc628..cce3575178e 100644
--- a/src/test/run-pass/deriving-global.rs
+++ b/src/test/run-pass/deriving-global.rs
@@ -28,19 +28,19 @@ mod submod {
     // cause errors about unrecognised module `std` (or `extra`)
     #[deriving(Eq, Ord, TotalEq, TotalOrd,
                Clone, DeepClone,
-               ToStr, Rand,
+               Show, Rand,
                Encodable, Decodable)]
     enum A { A1(uint), A2(int) }
 
     #[deriving(Eq, Ord, TotalEq, TotalOrd,
                Clone, DeepClone,
-               ToStr, Rand,
+               Show, Rand,
                Encodable, Decodable)]
     struct B { x: uint, y: int }
 
     #[deriving(Eq, Ord, TotalEq, TotalOrd,
                Clone, DeepClone,
-               ToStr, Rand,
+               Show, Rand,
                Encodable, Decodable)]
     struct C(uint, int);
 
diff --git a/src/test/run-pass/deriving-in-fn.rs b/src/test/run-pass/deriving-in-fn.rs
index 7fb7d601b81..baa036ee039 100644
--- a/src/test/run-pass/deriving-in-fn.rs
+++ b/src/test/run-pass/deriving-in-fn.rs
@@ -9,11 +9,11 @@
 // except according to those terms.
 
 pub fn main() {
-    #[deriving(ToStr)]
+    #[deriving(Show)]
     struct Foo {
         foo: int,
     }
 
     let f = Foo { foo: 10 };
-    let _ = f.to_str();
+    format!("{}", f);
 }
diff --git a/src/test/run-pass/deriving-to-str.rs b/src/test/run-pass/deriving-show-2.rs
similarity index 71%
rename from src/test/run-pass/deriving-to-str.rs
rename to src/test/run-pass/deriving-show-2.rs
index d9f69bd4a49..a2451c39400 100644
--- a/src/test/run-pass/deriving-to-str.rs
+++ b/src/test/run-pass/deriving-show-2.rs
@@ -10,30 +10,34 @@
 
 #[feature(struct_variant)];
 
-#[deriving(ToStr)]
+use std::fmt;
+
+#[deriving(Show)]
 enum A {}
-#[deriving(ToStr)]
+#[deriving(Show)]
 enum B { B1, B2, B3 }
-#[deriving(ToStr)]
+#[deriving(Show)]
 enum C { C1(int), C2(B), C3(~str) }
-#[deriving(ToStr)]
+#[deriving(Show)]
 enum D { D1{ a: int } }
-#[deriving(ToStr)]
+#[deriving(Show)]
 struct E;
-#[deriving(ToStr)]
+#[deriving(Show)]
 struct F(int);
-#[deriving(ToStr)]
+#[deriving(Show)]
 struct G(int, int);
-#[deriving(ToStr)]
+#[deriving(Show)]
 struct H { a: int }
-#[deriving(ToStr)]
+#[deriving(Show)]
 struct I { a: int, b: int }
-#[deriving(ToStr)]
+#[deriving(Show)]
 struct J(Custom);
 
 struct Custom;
-impl ToStr for Custom {
-    fn to_str(&self) -> ~str { ~"yay" }
+impl fmt::Show for Custom {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f.buf, "yay")
+    }
 }
 
 pub fn main() {
@@ -41,11 +45,11 @@ pub fn main() {
     assert_eq!(B2.to_str(), ~"B2");
     assert_eq!(C1(3).to_str(), ~"C1(3)");
     assert_eq!(C2(B2).to_str(), ~"C2(B2)");
-    assert_eq!(D1{ a: 2 }.to_str(), ~"D1{a: 2}");
+    assert_eq!(D1{ a: 2 }.to_str(), ~"D1 { a: 2 }");
     assert_eq!(E.to_str(), ~"E");
     assert_eq!(F(3).to_str(), ~"F(3)");
     assert_eq!(G(3, 4).to_str(), ~"G(3, 4)");
     assert_eq!(G(3, 4).to_str(), ~"G(3, 4)");
-    assert_eq!(I{ a: 2, b: 4 }.to_str(), ~"I{a: 2, b: 4}");
+    assert_eq!(I{ a: 2, b: 4 }.to_str(), ~"I { a: 2, b: 4 }");
     assert_eq!(J(Custom).to_str(), ~"J(yay)");
 }
diff --git a/src/test/run-pass/issue-2904.rs b/src/test/run-pass/issue-2904.rs
index 2816609ef97..45f59fe9cd4 100644
--- a/src/test/run-pass/issue-2904.rs
+++ b/src/test/run-pass/issue-2904.rs
@@ -17,7 +17,7 @@
 extern crate extra;
 
 use std::io;
-use std::to_str;
+use std::fmt;
 
 enum square {
     bot,
@@ -30,9 +30,9 @@ enum square {
     empty
 }
 
-impl to_str::ToStr for square {
-    fn to_str(&self) -> ~str {
-        match *self {
+impl fmt::Show for square {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f.buf, "{}", match *self {
           bot => { ~"R" }
           wall => { ~"#" }
           rock => { ~"*" }
@@ -41,7 +41,7 @@ impl to_str::ToStr for square {
           open_lift => { ~"O" }
           earth => { ~"." }
           empty => { ~" " }
-        }
+        })
     }
 }
 
diff --git a/src/test/run-pass/issue-3563-3.rs b/src/test/run-pass/issue-3563-3.rs
index 8e5dd762c63..ae65c46ce71 100644
--- a/src/test/run-pass/issue-3563-3.rs
+++ b/src/test/run-pass/issue-3563-3.rs
@@ -22,6 +22,7 @@ extern crate extra;
 // already linked in. Using WriterUtil allows us to use the write_line method.
 use std::str;
 use std::vec;
+use std::fmt;
 
 // Represents a position on a canvas.
 struct Point {
@@ -94,13 +95,13 @@ impl AsciiArt {
 
 // Allows AsciiArt to be converted to a string using the libcore ToStr trait.
 // Note that the %s fmt! specifier will not call this automatically.
-impl ToStr for AsciiArt {
-    fn to_str(&self) -> ~str {
+impl fmt::Show for AsciiArt {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         // Convert each line into a string.
         let lines = self.lines.map(|line| str::from_chars(*line));
 
         // Concatenate the lines together using a new-line.
-        lines.connect("\n")
+        write!(f.buf, "{}", lines.connect("\n"))
     }
 }
 
diff --git a/src/test/run-pass/new-impl-syntax.rs b/src/test/run-pass/new-impl-syntax.rs
index 6def21a389a..30200d4cb18 100644
--- a/src/test/run-pass/new-impl-syntax.rs
+++ b/src/test/run-pass/new-impl-syntax.rs
@@ -8,14 +8,16 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+use std::fmt;
+
 struct Thingy {
     x: int,
     y: int
 }
 
-impl ToStr for Thingy {
-    fn to_str(&self) -> ~str {
-        format!("\\{ x: {}, y: {} \\}", self.x, self.y)
+impl fmt::Show for Thingy {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f.buf, "\\{ x: {}, y: {} \\}", self.x, self.y)
     }
 }
 
@@ -23,9 +25,9 @@ struct PolymorphicThingy<T> {
     x: T
 }
 
-impl<T:ToStr> ToStr for PolymorphicThingy<T> {
-    fn to_str(&self) -> ~str {
-        self.x.to_str()
+impl<T:fmt::Show> fmt::Show for PolymorphicThingy<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f.buf, "{}", self.x)
     }
 }