diff --git a/and.rb b/and.rb
new file mode 100644
index 0000000..a42cfdd
--- /dev/null
+++ b/and.rb
@@ -0,0 +1,21 @@
+require_relative "gate.rb"
+require_relative "port.rb"
+
+# Represents an AND gate
+class AndGate < Gate
+
+  # Called when inputs change.
+  # Calculates AND of all inputs and sets output port to that value.
+  # @param vals [Array<Integer>] List of values for connected ports.
+  def inputs_changed(vals)
+    andval=nil
+    vals.each do |val|
+      if andval==nil
+        andval=val
+      else
+        andval=andval&val
+      end
+    end
+    out.setval(andval)
+  end
+end
diff --git a/gate.rb b/gate.rb
index 5eeb3c0..a2897da 100644
--- a/gate.rb
+++ b/gate.rb
@@ -41,6 +41,28 @@ class Gate
     inputs_changed(vals)
   end
 
+  # Test a truth table for a gate.
+  # @param table [Array<Array<Integer>>] The truth table,
+  #   which is an array of entries. The last value in the entry is the expected output,
+  #   the rest are the inputs to the ports.
+  def self.test_table(table)
+    ports=[]
+    (table[0].length-1).times do
+      ports.push Port.new(1)
+    end
+    gate=self.new(*ports)
+    table.each do |entry|
+      i=0
+      ports.each do |port|
+        port.setval(entry[i])
+        i+=1
+      end
+      return false if gate.out!=entry.last
+    end
+    return true
+  end
+
+  # Called when inputs change.
   # @abstract Override this to implement a gate.
   # @param vals [Array<Integer>] List of values for connected ports.
   def inputs_changed(vals); raise NotImplementedError; end
diff --git a/not.rb b/not.rb
new file mode 100644
index 0000000..2cfaf6a
--- /dev/null
+++ b/not.rb
@@ -0,0 +1,30 @@
+require_relative "gate.rb"
+require_relative "port.rb"
+
+# Represents a NOT gate
+class NotGate < Gate
+
+  # (see Gate#initialize)
+  def initialize(*args)
+    @outmask=0
+    super
+    @outmask=(2**@width)-1
+  end
+
+  # Add a port to the gate. As this is a NOT gate, there may only be one port.
+  # @param (see Gate#add_input)
+  # @return [void]
+  def add_input(input_port)
+    if @inputs.length > 0 then
+      raise ArgumentError, "Cannot add multiple inputs to a NOT gate"
+    end
+    super
+  end
+
+  # Called when inputs change.
+  #  Calculates NOT of input and sets output port to that value.
+  # @param vals [Array<Integer>] List of values for connected ports.
+  def inputs_changed(vals)
+    out.setval((~vals[0]) & @outmask)
+  end
+end
diff --git a/or.rb b/or.rb
new file mode 100644
index 0000000..2e1517c
--- /dev/null
+++ b/or.rb
@@ -0,0 +1,20 @@
+require_relative "gate.rb"
+require_relative "port.rb"
+
+# Represents an OR gate
+class OrGate < Gate
+
+  # Called when inputs change.
+  # Calculates OR of all inputs and sets output port to that value.
+  def inputs_changed(vals)
+    orval=nil
+    vals.each do |val|
+      if orval==nil
+        orval=val
+      else
+        orval=orval|val
+      end
+    end
+    out.setval(orval)
+  end
+end
diff --git a/spec/gate_spec.rb b/spec/gate_spec.rb
index 1f11e22..6ef6b23 100644
--- a/spec/gate_spec.rb
+++ b/spec/gate_spec.rb
@@ -1,6 +1,9 @@
-require_relative "../gate.rb"
 require_relative "../port.rb"
-
+require_relative "../gate.rb"
+require_relative "../not.rb"
+require_relative "../and.rb"
+require_relative "../or.rb"
+require_relative "../xor.rb"
 describe Gate do
   let(:klass) do
     Class.new(Gate) do
@@ -31,4 +34,54 @@ describe Gate do
     b.setval(10)
     expect(gate.out.val).to eq(18)
   end
+
+  context "NotGate" do
+    it "should NOT the input" do
+      table=[
+        [0,1],
+        [1,0]
+      ]
+      ok=NotGate.test_table(table)
+      expect(ok).to eq true
+    end
+  end
+
+  context "AndGate" do
+    it "should AND together all inputs" do
+      table=[
+        [0,0,0],
+        [0,1,0],
+        [1,0,0],
+        [1,1,1],
+      ]
+      ok=AndGate.test_table(table)
+      expect(ok).to eq true
+    end
+  end
+
+  context "OrGate" do
+    it "should OR together all inputs" do
+      table=[
+        [0,0,0],
+        [0,1,1],
+        [1,0,1],
+        [1,1,1],
+      ]
+      ok=OrGate.test_table(table)
+      expect(ok).to eq true
+    end
+  end
+
+  context "XorGate" do
+    it "should XOR together all inputs" do
+      table=[
+        [0,0,0],
+        [0,1,1],
+        [1,0,1],
+        [1,1,0],
+      ]
+      ok=XorGate.test_table(table)
+      expect(ok).to eq true
+    end
+  end
 end
diff --git a/xor.rb b/xor.rb
new file mode 100644
index 0000000..3e9728c
--- /dev/null
+++ b/xor.rb
@@ -0,0 +1,20 @@
+require_relative "gate.rb"
+require_relative "port.rb"
+
+# Represents an XOR gate
+class XorGate < Gate
+
+  # Called when inputs change.
+  # Calculates XOR of all inputs and sets output port to that value.
+  def inputs_changed(vals)
+    xorval=nil
+    vals.each do |val|
+      if xorval==nil
+        xorval=val
+      else
+        xorval=xorval^val
+      end
+    end
+    out.setval(xorval)
+  end
+end