diff --git a/lib/active_model/serializer.rb b/lib/active_model/serializer.rb
index aece7a47..ea3b4b6c 100644
--- a/lib/active_model/serializer.rb
+++ b/lib/active_model/serializer.rb
@@ -1,15 +1,18 @@
+require 'active_model/serializer/associations'
+
 module ActiveModel
   class Serializer
     class << self
       def inherited(base)
-        base._attributes = {}
+        base._attributes = []
+        base._associations = []
       end
 
       def serializer_for(resource)
         "#{resource.class.name}Serializer".safe_constantize
       end
 
-      attr_accessor :_root, :_attributes
+      attr_accessor :_root, :_attributes, :_associations
 
       def root(root)
         @_root = root
@@ -21,7 +24,7 @@ module ActiveModel
       end
 
       def attributes(*attrs)
-        @_attributes = attrs.map(&:to_s)
+        @_attributes.concat attrs.map(&:to_s)
 
         attrs.each do |attr|
           unless method_defined?(attr)
@@ -31,6 +34,22 @@ module ActiveModel
           end
         end
       end
+
+      def has_one(*attrs)
+        options = attrs.extract_options!
+
+        attrs.each do |attr|
+          attr = attr.to_s
+
+          unless method_defined?(attr)
+            define_method attr do
+              object.send attr
+            end
+          end
+
+          @_associations << Association::HasOne.new(attr, options)
+        end
+      end
     end
 
     def initialize(object, options={})
@@ -51,9 +70,30 @@ module ActiveModel
       end
     end
 
+    def associations
+      self.class._associations.each_with_object({}) do |association, hash|
+        if association.embed_ids?
+          hash[association.key] = serialize_ids association
+        elsif association.embed_objects?
+          # TODO
+          hash
+        end
+      end
+    end
+
+    def serialize_ids(association)
+      associated_data = send(association.name)
+      if associated_data.respond_to?(:to_ary)
+        associated_data.map { |elem| elem.send(association.embed_key) }
+      else
+        associated_data.send(association.embed_key)
+      end
+    end
+
     def serializable_hash(options={})
       return nil if object.nil?
-      attributes
+      hash = attributes
+      hash.merge! associations
     end
 
     def as_json(options={})
diff --git a/lib/active_model/serializer/associations.rb b/lib/active_model/serializer/associations.rb
new file mode 100644
index 00000000..a8bb4167
--- /dev/null
+++ b/lib/active_model/serializer/associations.rb
@@ -0,0 +1,43 @@
+module ActiveModel
+  class Serializer
+    class Association
+      def initialize(name, options={})
+        @name          = name
+        @options       = options
+
+        self.embed = options[:embed]
+        @embed_key = options[:embed_key] || :id
+        @include   = options[:include]
+
+        serializer = @options[:serializer]
+        @serializer_class = serializer.is_a?(String) ? serializer.constantize : serializer
+      end
+
+      attr_reader :name, :embed_ids, :embed_objects, :embed_key, :include
+      alias embed_ids? embed_ids
+      alias embed_objects? embed_objects
+      alias include? include
+
+      def embed=(embed)
+        @embed_ids     = embed == :id || embed == :ids
+        @embed_objects = embed == :object || embed == :objects
+      end
+
+      def build_serializer(object)
+        @serializer_class ||= Serializer.serializer_for(object)
+
+        if @serializer_class
+          @serializer_class.new(object, @options)
+        else
+          object
+        end
+      end
+
+      class HasOne < Association
+        def key
+          "#{name}_id"
+        end
+      end
+    end
+  end
+end
diff --git a/test/fixtures/poro.rb b/test/fixtures/poro.rb
index 4d5850be..10586934 100644
--- a/test/fixtures/poro.rb
+++ b/test/fixtures/poro.rb
@@ -6,6 +6,14 @@ class Model
   def read_attribute_for_serialization(name)
     @attributes[name]
   end
+
+  def model
+    @model ||= Model.new(attr1: 'v1', attr2: 'v2')
+  end
+
+  def id
+    object_id
+  end
 end
 
 class ModelSerializer < ActiveModel::Serializer
@@ -20,3 +28,9 @@ class ModelSerializer < ActiveModel::Serializer
 
   attributes :attr1, :attr2
 end
+
+class AnotherSerializer < ActiveModel::Serializer
+  attributes :attr2, :attr3
+
+  has_one :model
+end
diff --git a/test/unit/active_model/serializer/has_one_test.rb b/test/unit/active_model/serializer/has_one_test.rb
new file mode 100644
index 00000000..652ed3e4
--- /dev/null
+++ b/test/unit/active_model/serializer/has_one_test.rb
@@ -0,0 +1,35 @@
+require 'test_helper'
+require 'active_model/serializer'
+
+module ActiveModel
+  class Serializer
+    class HasOneTest < ActiveModel::TestCase
+      def setup
+        @model = ::Model.new({ :attr1 => 'value1', :attr2 => 'value2', :attr3 => 'value3' })
+        @model_serializer = AnotherSerializer.new(@model)
+      end
+
+      def test_associations_definition
+        associations = @model_serializer.class._associations
+
+        assert_equal 1, associations.length
+        assert_kind_of Association::HasOne, associations[0]
+        assert_equal 'model', associations[0].name
+      end
+
+      def test_associations_serialization_using_serializable_hash
+        @model_serializer.class._associations[0].embed = :ids
+        assert_equal({
+          'attr2' => 'value2', 'attr3' => 'value3', 'model_id' => @model.model.object_id
+        }, @model_serializer.serializable_hash)
+      end
+
+      def test_associations_serialization_using_as_json
+        @model_serializer.class._associations[0].embed = :ids
+        assert_equal({
+          'attr2' => 'value2', 'attr3' => 'value3', 'model_id' => @model.model.object_id
+        }, @model_serializer.as_json)
+      end
+    end
+  end
+end