diff --git a/README b/README
index 215097a..45e5b44 100644
--- a/README
+++ b/README
@@ -34,16 +34,20 @@ a block instead of a parameter:
     u.activation_code { User.generate_activation_code }
   end
 
-== Using factories
+== Dependent Attributes
 
-  # Build and save a User instance
-  Factory(:user)
+Some attributes may need to be generated based on the values of other
+attributes. This can be done by calling the attribute name on
+Factory::AttributeProxy, which is yielded to lazy attribute blocks:
 
-  # Build a User instance and override the first_name property
-  Factory.build(:user, :first_name => 'Joe')
+  Factory.define :user do |u|
+    u.first_name 'Joe'
+    u.last_name  'Blow'
+    u.email {|a| "#{a.first_name}.#{a.last_name}@example.com".downcase }
+  end
 
-  # Return an attributes Hash that can be used to build a User instance
-  attrs = Factory.attributes_for(:user)
+  Factory(:user, :last_name => 'Doe').email
+  # => "joe.doe@example.com"
 
 == Associations
 
@@ -66,3 +70,15 @@ When using the association method, the same build strategy (build, create, or at
   Factory.build(:post)
   post.new_record?       # => true
   post.author.new_record # => true
+
+== Using factories
+
+  # Build and save a User instance
+  Factory(:user)
+
+  # Build a User instance and override the first_name property
+  Factory.build(:user, :first_name => 'Joe')
+
+  # Return an attributes Hash that can be used to build a User instance
+  attrs = Factory.attributes_for(:user)
+
diff --git a/lib/factory_girl/attribute_proxy.rb b/lib/factory_girl/attribute_proxy.rb
index 58fe23a..d19a286 100644
--- a/lib/factory_girl/attribute_proxy.rb
+++ b/lib/factory_girl/attribute_proxy.rb
@@ -2,12 +2,13 @@ class Factory
 
   class AttributeProxy
 
-    attr_accessor :factory, :attribute_name, :strategy #:nodoc:
+    attr_accessor :factory, :attribute_name, :strategy, :current_values #:nodoc:
 
-    def initialize (factory, attr, strategy) #:nodoc:
+    def initialize (factory, attr, strategy, values) #:nodoc:
       @factory        = factory
       @attribute_name = attr
       @strategy       = strategy
+      @current_values = values
     end
 
     # Generates an association using the current build strategy.
@@ -34,6 +35,42 @@ class Factory
       Factory.send(strategy, name, attributes)
     end
 
+    # Returns the value for specified attribute. A value will only be available
+    # if it was overridden when calling the factory, or if a value is added
+    # earlier in the definition of the factory.
+    #
+    # Arguments:
+    #   attribute: (Symbol)
+    #     The attribute whose value should be returned.
+    #
+    # Returns:
+    #   The value of the requested attribute. (Object)
+    def value_for (attribute)
+      unless current_values.key?(attribute)
+        raise ArgumentError, "No such attribute: #{attribute.inspect}"
+      end
+      current_values[attribute]
+    end
+
+    # Undefined methods are delegated to value_for, which means that:
+    #
+    #   Factory.define :user do |f|
+    #     f.first_name 'Ben'
+    #     f.last_name {|a| a.value_for(:first_name) }
+    #   end
+    #
+    # and:
+    #
+    #   Factory.define :user do |f|
+    #     f.first_name 'Ben'
+    #     f.last_name {|a| a.first_name }
+    #   end
+    #
+    # are equivilent.
+    def method_missing (name, *args, &block)
+      current_values[name]
+    end
+
   end
 
 end
diff --git a/lib/factory_girl/factory.rb b/lib/factory_girl/factory.rb
index 9f37b7d..0ec799f 100644
--- a/lib/factory_girl/factory.rb
+++ b/lib/factory_girl/factory.rb
@@ -33,8 +33,9 @@ class Factory
     @name    = name
     @options = options
 
-    @static_attributes = {}
-    @lazy_attributes   = {}
+    @static_attributes     = {}
+    @lazy_attribute_blocks = {}
+    @lazy_attribute_names  = []
   end
 
   # Adds an attribute that should be assigned on generated instances for this
@@ -60,7 +61,8 @@ class Factory
       unless value.nil?
         raise ArgumentError, "Both value and block given"
       end
-      @lazy_attributes[name] = block
+      @lazy_attribute_blocks[name] = block
+      @lazy_attribute_names << name
     else
       @static_attributes[name] = value
     end
@@ -158,13 +160,12 @@ class Factory
   private
 
   def build_attributes_hash (override, strategy)
-    result = {}
-    @lazy_attributes.each do |name, block|
-      proxy = AttributeProxy.new(self, name, strategy)
-      result[name] = block.call(proxy) unless override.key?(name)
+    result = @static_attributes.merge(override)
+    @lazy_attribute_names.each do |name|
+      proxy = AttributeProxy.new(self, name, strategy, result)
+      result[name] = @lazy_attribute_blocks[name].call(proxy) unless override.key?(name)
     end
-    result.update(@static_attributes)
-    result.update(override)
+    result
   end
 
   def build_instance (override, strategy)
diff --git a/test/attribute_proxy_test.rb b/test/attribute_proxy_test.rb
index 0298500..fabfb73 100644
--- a/test/attribute_proxy_test.rb
+++ b/test/attribute_proxy_test.rb
@@ -7,8 +7,9 @@ class AttributeProxyTest < Test::Unit::TestCase
     setup do
       @factory  = mock('factory')
       @attr     = :user
+      @attrs    = { :first_name => 'John' }
       @strategy = :create
-      @proxy  = Factory::AttributeProxy.new(@factory, @attr, @strategy)
+      @proxy  = Factory::AttributeProxy.new(@factory, @attr, @strategy, @attrs)
     end
 
     should "have a factory" do
@@ -23,6 +24,10 @@ class AttributeProxyTest < Test::Unit::TestCase
       assert_equal @strategy, @proxy.strategy
     end
 
+    should "have attributes" do
+      assert_equal @attrs, @proxy.current_values
+    end
+
     context "building an association" do
 
       setup do
@@ -44,6 +49,34 @@ class AttributeProxyTest < Test::Unit::TestCase
 
     end
 
+    context "fetching the value of an attribute" do
+
+      setup do
+        @attr = :first_name
+      end
+
+      should "return the correct value" do
+        assert_equal @attrs[@attr], @proxy.value_for(@attr)
+      end
+
+      should "call value_for for undefined methods" do
+        assert_equal @attrs[@attr], @proxy.send(@attr)
+      end
+
+    end
+
+    context "fetching the value of an undefined attribute" do
+
+      setup do
+        @attr = :beachball
+      end
+
+      should "raise an ArgumentError" do
+        assert_raise(ArgumentError) { @proxy.value_for(@attr) }
+      end
+
+    end
+
   end
 
 end
diff --git a/test/factory_test.rb b/test/factory_test.rb
index be5018a..943abaa 100644
--- a/test/factory_test.rb
+++ b/test/factory_test.rb
@@ -86,6 +86,7 @@ class FactoryTest < Test::Unit::TestCase
 
       setup do
         @attr  = :name
+        @attrs = {}
         @proxy = mock('attr-proxy')
         Factory::AttributeProxy.stubs(:new).returns(@proxy)
       end
@@ -110,7 +111,7 @@ class FactoryTest < Test::Unit::TestCase
       end
 
       should "build an attribute proxy" do
-        Factory::AttributeProxy.expects(:new).with(@factory, @attr, :attributes_for)
+        Factory::AttributeProxy.expects(:new).with(@factory, @attr, :attributes_for, @attrs)
         @factory.add_attribute(@attr) {}
         @factory.attributes_for
       end
@@ -122,6 +123,26 @@ class FactoryTest < Test::Unit::TestCase
         assert_equal @proxy, yielded
       end
 
+      context "when other attributes have previously been defined" do
+        
+        setup do
+          @attr  = :unimportant
+          @attrs = {
+            :one     => 'whatever',
+            :another => 'soup'
+          }
+          @factory.add_attribute(:one, 'whatever')
+          @factory.add_attribute(:another) { 'soup' }
+          @factory.add_attribute(@attr) {}
+        end
+
+        should "provide previously set attributes" do
+          Factory::AttributeProxy.expects(:new).with(@factory, @attr, :attributes_for, @attrs)
+          @factory.attributes_for
+        end
+
+      end
+
     end
 
     should "add an attribute using the method name when passed an undefined method" do