diff --git a/GETTING_STARTED.md b/GETTING_STARTED.md
index 2f3fe98c2..1d5850508 100644
--- a/GETTING_STARTED.md
+++ b/GETTING_STARTED.md
@@ -590,6 +590,42 @@ To set the attributes for each of the factories, you can pass in a hash as you n
 twenty_year_olds = FactoryGirl.build_list(:user, 25, :date_of_birth => 20.years.ago)
 ```
 
+Custom Construction
+-------------------
+
+Instantiating objects can be overridden in the case where you'd rather not
+call `new` on your build class or you have some other factory method that
+you'd prefer to use. Using custom construction also allows for your objects to
+be instantiated with any number of arguments.
+
+```ruby
+# user.rb
+class User
+  attr_accessor :name, :email
+
+  def initialize(name)
+    @name = name
+  end
+end
+
+# factories.rb
+sequence(:name) {|n| "person#{n}@example.com" }
+
+factory :user do
+  ignore do
+    name { Faker::Name.name }
+  end
+
+  email
+  initialize_with { User.new(name) }
+end
+
+FactoryGirl.build(:user).name # Bob Hope
+```
+
+Notice that I ignored the `name` attribute. If you don't want attributes
+reassigned after your object has been instantiated, you'll want to `ignore` them.
+
 Cucumber Integration
 --------------------
 
@@ -620,4 +656,4 @@ User.blueprint do
 end
 
 User.make(:name => 'Johnny')
-```
\ No newline at end of file
+```
diff --git a/lib/factory_girl/attribute_assigner.rb b/lib/factory_girl/attribute_assigner.rb
index b93b51094..701f63e3a 100644
--- a/lib/factory_girl/attribute_assigner.rb
+++ b/lib/factory_girl/attribute_assigner.rb
@@ -1,7 +1,7 @@
 module FactoryGirl
   class AttributeAssigner
-    def initialize(build_class, evaluator)
-      @build_class              = build_class
+    def initialize(evaluator, &instance_builder)
+      @instance_builder         = instance_builder
       @evaluator                = evaluator
       @attribute_list           = evaluator.class.attribute_list
       @attribute_names_assigned = []
@@ -29,7 +29,7 @@ def hash
     private
 
     def build_class_instance
-      @build_class_instance ||= @build_class.new
+      @build_class_instance ||= @evaluator.instance_exec(&@instance_builder)
     end
 
     def get(attribute_name)
diff --git a/lib/factory_girl/definition.rb b/lib/factory_girl/definition.rb
index 222773c52..4cf3564a4 100644
--- a/lib/factory_girl/definition.rb
+++ b/lib/factory_girl/definition.rb
@@ -1,6 +1,6 @@
 module FactoryGirl
   class Definition
-    attr_reader :callbacks, :defined_traits, :declarations
+    attr_reader :callbacks, :defined_traits, :declarations, :constructor
 
     def initialize(name = nil, base_traits = [])
       @declarations      = DeclarationList.new(name)
@@ -9,6 +9,7 @@ def initialize(name = nil, base_traits = [])
       @to_create         = lambda {|instance| instance.save! }
       @base_traits       = base_traits
       @additional_traits = []
+      @constructor       = nil
     end
 
     delegate :declare_attribute, :to => :declarations
@@ -50,6 +51,10 @@ def define_trait(trait)
       @defined_traits << trait
     end
 
+    def define_constructor(&block)
+      @constructor = block
+    end
+
     private
 
     def base_traits
diff --git a/lib/factory_girl/definition_proxy.rb b/lib/factory_girl/definition_proxy.rb
index ad2e5c4d8..72e4af53b 100644
--- a/lib/factory_girl/definition_proxy.rb
+++ b/lib/factory_girl/definition_proxy.rb
@@ -161,5 +161,9 @@ def factory(name, options = {}, &block)
     def trait(name, &block)
       @definition.define_trait(Trait.new(name, &block))
     end
+
+    def initialize_with(&block)
+      @definition.define_constructor(&block)
+    end
   end
 end
diff --git a/lib/factory_girl/factory.rb b/lib/factory_girl/factory.rb
index c3e7d1d2e..c457e2fe7 100644
--- a/lib/factory_girl/factory.rb
+++ b/lib/factory_girl/factory.rb
@@ -43,7 +43,7 @@ def run(proxy_class, overrides, &block) #:nodoc:
       proxy = proxy_class.new
 
       evaluator = evaluator_class.new(proxy, overrides.symbolize_keys)
-      attribute_assigner = AttributeAssigner.new(build_class, evaluator)
+      attribute_assigner = AttributeAssigner.new(evaluator, &instance_builder)
 
       proxy.result(attribute_assigner, to_create).tap(&block)
     end
@@ -123,6 +123,10 @@ def callbacks
       processing_order.map {|factory| factory.callbacks }.flatten
     end
 
+    def constructor
+      @constructor ||= @definition.constructor || parent.constructor
+    end
+
     private
 
     def assert_valid_options(options)
@@ -143,6 +147,11 @@ def parent
       end
     end
 
+    def instance_builder
+      build_class = self.build_class
+      constructor || lambda { build_class.new }
+    end
+
     def initialize_copy(source)
       super
       @definition = @definition.clone
diff --git a/lib/factory_girl/null_factory.rb b/lib/factory_girl/null_factory.rb
index 2a7d9a77d..5e812461c 100644
--- a/lib/factory_girl/null_factory.rb
+++ b/lib/factory_girl/null_factory.rb
@@ -6,7 +6,7 @@ def initialize
       @definition = Definition.new
     end
 
-    delegate :defined_traits, :callbacks, :attributes, :to => :definition
+    delegate :defined_traits, :callbacks, :attributes, :constructor, :to => :definition
 
     def compile; end
     def class_name; end
diff --git a/spec/acceptance/initialize_with_spec.rb b/spec/acceptance/initialize_with_spec.rb
new file mode 100644
index 000000000..a5305ed4e
--- /dev/null
+++ b/spec/acceptance/initialize_with_spec.rb
@@ -0,0 +1,147 @@
+require "spec_helper"
+
+describe "initialize_with with non-FG attributes" do
+  include FactoryGirl::Syntax::Methods
+
+  before do
+    define_model("User", :name => :string, :age => :integer) do
+      def self.construct(name, age)
+        new(:name => name, :age => age)
+      end
+    end
+
+    FactoryGirl.define do
+      factory :user do
+        initialize_with { User.construct("John Doe", 21) }
+      end
+    end
+  end
+
+  subject    { build(:user) }
+  its(:name) { should == "John Doe" }
+  its(:age)  { should == 21 }
+end
+
+describe "initialize_with with FG attributes that are ignored" do
+  include FactoryGirl::Syntax::Methods
+
+  before do
+    define_model("User", :name => :string) do
+      def self.construct(name)
+        new(:name => "#{name} from .construct")
+      end
+    end
+
+    FactoryGirl.define do
+      factory :user do
+        ignore do
+          name { "Handsome Chap" }
+        end
+
+        initialize_with { User.construct(name) }
+      end
+    end
+  end
+
+  subject    { build(:user) }
+  its(:name) { should == "Handsome Chap from .construct" }
+end
+
+describe "initialize_with with FG attributes that are not ignored" do
+  include FactoryGirl::Syntax::Methods
+
+  before do
+    define_model("User", :name => :string) do
+      def self.construct(name)
+        new(:name => "#{name} from .construct")
+      end
+    end
+
+    FactoryGirl.define do
+      factory :user do
+        name { "Handsome Chap" }
+
+        initialize_with { User.construct(name) }
+      end
+    end
+  end
+
+  it "assigns each attribute even if the attribute has been used in the constructor" do
+    build(:user).name.should == "Handsome Chap"
+  end
+end
+
+describe "initialize_with non-ORM-backed objects" do
+  include FactoryGirl::Syntax::Methods
+
+  before do
+    define_class("ReportGenerator") do
+      attr_reader :name, :data
+
+      def initialize(name, data)
+        @name = name
+        @data = data
+      end
+    end
+
+    FactoryGirl.define do
+      sequence(:random_data) { 5.times.map { Kernel.rand(200) } }
+
+      factory :report_generator do
+        ignore do
+          name "My Awesome Report"
+        end
+
+        initialize_with { ReportGenerator.new(name, FactoryGirl.generate(:random_data)) }
+      end
+    end
+  end
+
+  it "allows for overrides" do
+    build(:report_generator, :name => "Overridden").name.should == "Overridden"
+  end
+
+  it "generates random data" do
+    build(:report_generator).data.length.should == 5
+  end
+end
+
+describe "initialize_with parent and child factories" do
+  before do
+    define_class("Awesome") do
+      attr_reader :name
+
+      def initialize(name)
+        @name = name
+      end
+    end
+
+    FactoryGirl.define do
+      factory :awesome do
+        ignore do
+          name "Great"
+        end
+
+        initialize_with { Awesome.new(name) }
+
+        factory :sub_awesome do
+          ignore do
+            name "Sub"
+          end
+        end
+
+        factory :super_awesome do
+          initialize_with { Awesome.new("Super") }
+        end
+      end
+    end
+  end
+
+  it "uses the parent's constructor when the child factory doesn't assign it" do
+    FactoryGirl.build(:sub_awesome).name.should == "Sub"
+  end
+
+  it "allows child factories to override initialize_with" do
+    FactoryGirl.build(:super_awesome).name.should == "Super"
+  end
+end
diff --git a/spec/factory_girl/definition_proxy_spec.rb b/spec/factory_girl/definition_proxy_spec.rb
index ddd3b92b8..d5870f2e8 100644
--- a/spec/factory_girl/definition_proxy_spec.rb
+++ b/spec/factory_girl/definition_proxy_spec.rb
@@ -184,3 +184,14 @@
     subject.should have_trait(:male).with_block(male_trait)
   end
 end
+
+describe FactoryGirl::DefinitionProxy, "#initialize_with" do
+  subject     { FactoryGirl::Definition.new }
+  let(:proxy) { FactoryGirl::DefinitionProxy.new(subject) }
+
+  it "defines the constructor on the definition" do
+    constructor = Proc.new { Array.new }
+    proxy.initialize_with(&constructor)
+    subject.constructor.should == constructor
+  end
+end
diff --git a/spec/factory_girl/null_factory_spec.rb b/spec/factory_girl/null_factory_spec.rb
index ead5614ef..f86ed6128 100644
--- a/spec/factory_girl/null_factory_spec.rb
+++ b/spec/factory_girl/null_factory_spec.rb
@@ -4,6 +4,7 @@
   it { should delegate(:defined_traits).to(:definition) }
   it { should delegate(:callbacks).to(:definition) }
   it { should delegate(:attributes).to(:definition) }
+  it { should delegate(:constructor).to(:definition) }
 
   its(:compile)          { should be_nil }
   its(:class_name)       { should be_nil }