diff --git a/README.md b/README.md
index 441a5379..d98ab729 100644
--- a/README.md
+++ b/README.md
@@ -57,7 +57,13 @@ by AMS. If you want to use a different adapter, such as a HalAdapter, you can
 change this in an initializer:
 
 ```ruby
-ActiveModel::Serializer.default_adapter = ActiveModel::Serializer::Adapter::HalAdapter
+ActiveModel::Serializer.config.adapter = ActiveModel::Serializer::Adapter::HalAdapter
+```
+
+or
+ 
+```ruby
+ActiveModel::Serializer.config.adapter = :hal
 ```
 
 You won't need to implement an adapter unless you wish to use a new format or
diff --git a/lib/action_controller/serialization.rb b/lib/action_controller/serialization.rb
index d51aba0f..a69109e5 100644
--- a/lib/action_controller/serialization.rb
+++ b/lib/action_controller/serialization.rb
@@ -12,7 +12,7 @@ module ActionController
       if serializer
         # omg hax
         object = serializer.new(resource)
-        adapter = ActiveModel::Serializer::Adapter::NullAdapter.new(object)
+        adapter = ActiveModel::Serializer.adapter.new(object)
 
         super(adapter, options)
       else
diff --git a/lib/active_model/serializer.rb b/lib/active_model/serializer.rb
index b94b8a46..05a79900 100644
--- a/lib/active_model/serializer.rb
+++ b/lib/active_model/serializer.rb
@@ -3,6 +3,7 @@ module ActiveModel
     extend ActiveSupport::Autoload
     autoload :Configuration
     autoload :ArraySerializer
+    autoload :Adapter
     include Configuration
 
     class << self
@@ -65,26 +66,49 @@ module ActiveModel
       if resource.respond_to?(:to_ary)
         config.array_serializer
       else
-        serializer_name = "#{resource.class.name}Serializer"
-
-        begin
-          Object.const_get(serializer_name)
-        rescue NameError
-          nil
-        end
+        serializer_class = "#{resource.class.name}Serializer"
+        serializer_class.safe_constantize
       end
     end
 
+    def self.adapter
+      adapter_class = case config.adapter
+                      when Symbol
+                        class_name = "ActiveModel::Serializer::Adapter::#{config.adapter.to_s.classify}"
+                        class_name.safe_constantize
+                      when Class
+                        config.adapter
+                      end
+      unless adapter_class
+        valid_adapters = Adapter.constants.map { |klass| ":#{klass.to_s.downcase}" }
+        raise ArgumentError, "Unknown adapter: #{config.adapter}. Valid adapters are: #{valid_adapters}"
+      end
+
+      adapter_class
+    end
+
     attr_accessor :object
 
     def initialize(object)
       @object = object
     end
 
-    def attributes
+    def attributes(options = {})
       self.class._attributes.dup.each_with_object({}) do |name, hash|
         hash[name] = send(name)
       end
     end
+
+    def each_association(&block)
+      self.class._associations.dup.each do |name, options|
+        association = object.send(name)
+        serializer_class = ActiveModel::Serializer.serializer_for(association)
+        serializer = serializer_class.new(association)
+
+        if block_given?
+          block.call(name, serializer, options[:options])
+        end
+      end
+    end
   end
 end
diff --git a/lib/active_model/serializer/adapter.rb b/lib/active_model/serializer/adapter.rb
new file mode 100644
index 00000000..2fae98ff
--- /dev/null
+++ b/lib/active_model/serializer/adapter.rb
@@ -0,0 +1,24 @@
+module ActiveModel
+  class Serializer
+    class Adapter
+      extend ActiveSupport::Autoload
+      autoload :Json
+      autoload :Null
+      autoload :JsonApi
+
+      attr_reader :serializer
+
+      def initialize(serializer)
+        @serializer = serializer
+      end
+
+      def serializable_hash(options = {})
+        raise NotImplementedError, 'This is an abstract method. Should be implemented at the concrete adapter.'
+      end
+
+      def to_json(options={})
+        serializable_hash(options).to_json
+      end
+    end
+  end
+end
diff --git a/lib/active_model/serializer/adapter/json.rb b/lib/active_model/serializer/adapter/json.rb
new file mode 100644
index 00000000..f37fc8d4
--- /dev/null
+++ b/lib/active_model/serializer/adapter/json.rb
@@ -0,0 +1,21 @@
+module ActiveModel
+  class Serializer
+    class Adapter
+      class Json < Adapter
+        def serializable_hash(options = {})
+          @hash = serializer.attributes(options)
+
+          serializer.each_association do |name, association, options|
+            if association.respond_to?(:each)
+              array_serializer = association
+              @hash[name] = array_serializer.map { |item| item.attributes(options) }
+            else
+              @hash[name] = association.attributes(options)
+            end
+          end
+          @hash
+        end
+      end
+    end
+  end
+end
diff --git a/lib/active_model/serializer/adapter/json_api.rb b/lib/active_model/serializer/adapter/json_api.rb
new file mode 100644
index 00000000..a4f516dc
--- /dev/null
+++ b/lib/active_model/serializer/adapter/json_api.rb
@@ -0,0 +1,39 @@
+module ActiveModel
+  class Serializer
+    class Adapter
+      class JsonApi < Adapter
+        def serializable_hash(options = {})
+          @hash = serializer.attributes
+
+          serializer.each_association do |name, association, options|
+            @hash[:links] ||= {}
+            @hash[:linked] ||= {}
+
+            if association.respond_to?(:each)
+              add_links(name, association, options)
+            else
+              add_link(name, association, options)
+            end
+          end
+
+          @hash
+        end
+
+        def add_links(name, serializers, options)
+          @hash[:links][name] ||= []
+          @hash[:linked][name] ||= []
+          @hash[:links][name] += serializers.map(&:id)
+          @hash[:linked][name] += serializers.map { |item| item.attributes(options) }
+        end
+
+        def add_link(name, serializer, options)
+          plural_name = name.to_s.pluralize.to_sym
+          @hash[:linked][plural_name] ||= []
+
+          @hash[:links][name] = serializer.id
+          @hash[:linked][plural_name].push serializer.attributes(options)
+        end
+      end
+    end
+  end
+end
diff --git a/lib/active_model/serializer/adapter/null.rb b/lib/active_model/serializer/adapter/null.rb
new file mode 100644
index 00000000..547c08ba
--- /dev/null
+++ b/lib/active_model/serializer/adapter/null.rb
@@ -0,0 +1,11 @@
+module ActiveModel
+  class Serializer
+    class Adapter
+      class Null < Adapter
+        def serializable_hash(options = {})
+          {}
+        end
+      end
+    end
+  end
+end
diff --git a/lib/active_model/serializer/adapter/null_adapter.rb b/lib/active_model/serializer/adapter/null_adapter.rb
deleted file mode 100644
index 7ef77f21..00000000
--- a/lib/active_model/serializer/adapter/null_adapter.rb
+++ /dev/null
@@ -1,17 +0,0 @@
-module ActiveModel
-  class Serializer
-    class Adapter
-      class NullAdapter
-        def initialize(adapter)
-          @attributes = adapter.attributes 
-        end
-
-        def to_json(options={})
-          @attributes.each_with_object({}) do |(attr, value), h|
-            h[attr] = value
-          end.to_json # FIXME: why does passing options here cause {}?
-        end
-      end
-    end
-  end
-end
diff --git a/lib/active_model/serializer/array_serializer.rb b/lib/active_model/serializer/array_serializer.rb
index d385d6bf..697c4454 100644
--- a/lib/active_model/serializer/array_serializer.rb
+++ b/lib/active_model/serializer/array_serializer.rb
@@ -1,7 +1,15 @@
 module ActiveModel
   class Serializer
     class ArraySerializer
+      include Enumerable
+      delegate :each, to: :@objects
 
+      def initialize(objects, options = {})
+        @objects = objects.map do |object|
+          serializer_class = ActiveModel::Serializer.serializer_for(object)
+          serializer_class.new(object)
+        end
+      end
     end
   end
 end
diff --git a/lib/active_model/serializer/configuration.rb b/lib/active_model/serializer/configuration.rb
index ac89443c..ef57262c 100644
--- a/lib/active_model/serializer/configuration.rb
+++ b/lib/active_model/serializer/configuration.rb
@@ -6,6 +6,7 @@ module ActiveModel
 
       included do |base|
         base.config.array_serializer = ActiveModel::Serializer::ArraySerializer
+        base.config.adapter = :json
       end
     end
   end
diff --git a/lib/active_model_serializers.rb b/lib/active_model_serializers.rb
index f7774290..c96b90a9 100644
--- a/lib/active_model_serializers.rb
+++ b/lib/active_model_serializers.rb
@@ -1,7 +1,6 @@
 require "active_model"
 require "active_model/serializer/version"
 require "active_model/serializer"
-require "active_model/serializer/adapter/null_adapter"
 
 begin
   require 'action_controller'
diff --git a/test/adapter/json/belongs_to_test.rb b/test/adapter/json/belongs_to_test.rb
new file mode 100644
index 00000000..498f1d98
--- /dev/null
+++ b/test/adapter/json/belongs_to_test.rb
@@ -0,0 +1,25 @@
+require 'test_helper'
+
+module ActiveModel
+  class Serializer
+    class Adapter
+      class Json
+        class BelongsToTest < Minitest::Test
+          def setup
+            @post = Post.new(id: 42, title: 'New Post', body: 'Body')
+            @comment = Comment.new(id: 1, body: 'ZOMG A COMMENT')
+            @post.comments = [@comment]
+            @comment.post = @post
+
+            @serializer = CommentSerializer.new(@comment)
+            @adapter = ActiveModel::Serializer::Adapter::Json.new(@serializer)
+          end
+
+          def test_includes_post
+            assert_equal({id: 42, title: 'New Post', body: 'Body'}, @adapter.serializable_hash[:post])
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/test/adapter/json/has_many_test.rb b/test/adapter/json/has_many_test.rb
new file mode 100644
index 00000000..d1534e6b
--- /dev/null
+++ b/test/adapter/json/has_many_test.rb
@@ -0,0 +1,31 @@
+require 'test_helper'
+
+module ActiveModel
+  class Serializer
+    class Adapter
+      class Json
+        class HasManyTestTest < Minitest::Test
+          def setup
+            @post = Post.new(title: 'New Post', body: 'Body')
+            @first_comment = Comment.new(id: 1, body: 'ZOMG A COMMENT')
+            @second_comment = Comment.new(id: 2, body: 'ZOMG ANOTHER COMMENT')
+            @post.comments = [@first_comment, @second_comment]
+            @first_comment.post = @post
+            @second_comment.post = @post
+
+            @serializer = PostSerializer.new(@post)
+            @adapter = ActiveModel::Serializer::Adapter::Json.new(@serializer)
+          end
+
+          def test_has_many
+            assert_equal([
+                           {id: 1, body: 'ZOMG A COMMENT'},
+                           {id: 2, body: 'ZOMG ANOTHER COMMENT'}
+                         ], @adapter.serializable_hash[:comments])
+          end
+        end
+      end
+    end
+  end
+end
+
diff --git a/test/adapter/json_api/belongs_to_test.rb b/test/adapter/json_api/belongs_to_test.rb
new file mode 100644
index 00000000..151fd8cc
--- /dev/null
+++ b/test/adapter/json_api/belongs_to_test.rb
@@ -0,0 +1,29 @@
+require 'test_helper'
+
+module ActiveModel
+  class Serializer
+    class Adapter
+      class JsonApi
+        class BelongsToTest < Minitest::Test
+          def setup
+            @post = Post.new(id: 42, title: 'New Post', body: 'Body')
+            @comment = Comment.new(id: 1, body: 'ZOMG A COMMENT')
+            @post.comments = [@comment]
+            @comment.post = @post
+
+            @serializer = CommentSerializer.new(@comment)
+            @adapter = ActiveModel::Serializer::Adapter::JsonApi.new(@serializer)
+          end
+
+          def test_includes_post_id
+            assert_equal(42, @adapter.serializable_hash[:links][:post])
+          end
+
+          def test_includes_linked_post
+            assert_equal([{id: 42, title: 'New Post', body: 'Body'}], @adapter.serializable_hash[:linked][:posts])
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/test/adapter/json_api/has_many.rb b/test/adapter/json_api/has_many.rb
new file mode 100644
index 00000000..435079d7
--- /dev/null
+++ b/test/adapter/json_api/has_many.rb
@@ -0,0 +1,34 @@
+require 'test_helper'
+
+module ActiveModel
+  class Serializer
+    class Adapter
+      class JsonApi
+        class HasManyTest < Minitest::Test
+          def setup
+            @post = Post.new(title: 'New Post', body: 'Body')
+            @first_comment = Comment.new(id: 1, body: 'ZOMG A COMMENT')
+            @second_comment = Comment.new(id: 2, body: 'ZOMG ANOTHER COMMENT')
+            @post.comments = [@first_comment, @second_comment]
+            @first_comment.post = @post
+            @second_comment.post = @post
+
+            @serializer = PostSerializer.new(@post)
+            @adapter = ActiveModel::Serializer::Adapter::JsonApi.new(@serializer)
+          end
+
+          def test_includes_comment_ids
+            assert_equal([1, 2], @adapter.serializable_hash[:links][:comments])
+          end
+
+          def test_includes_linked_comments
+            assert_equal([
+                           {id: 1, body: 'ZOMG A COMMENT'},
+                           {id: 2, body: 'ZOMG ANOTHER COMMENT'}
+                         ], @adapter.serializable_hash[:linked][:comments])
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/test/adapter/json_test.rb b/test/adapter/json_test.rb
new file mode 100644
index 00000000..1d2e35a6
--- /dev/null
+++ b/test/adapter/json_test.rb
@@ -0,0 +1,29 @@
+require 'test_helper'
+
+module ActiveModel
+  class Serializer
+    class Adapter
+      class JsonTest < Minitest::Test
+        def setup
+          @post = Post.new(title: 'New Post', body: 'Body')
+          @first_comment = Comment.new(id: 1, body: 'ZOMG A COMMENT')
+          @second_comment = Comment.new(id: 2, body: 'ZOMG ANOTHER COMMENT')
+          @post.comments = [@first_comment, @second_comment]
+          @first_comment.post = @post
+          @second_comment.post = @post
+
+          @serializer = PostSerializer.new(@post)
+          @adapter = ActiveModel::Serializer::Adapter::Json.new(@serializer)
+        end
+
+        def test_has_many
+          assert_equal([
+                         {id: 1, body: 'ZOMG A COMMENT'},
+                         {id: 2, body: 'ZOMG ANOTHER COMMENT'}
+                       ], @adapter.serializable_hash[:comments])
+        end
+      end
+    end
+  end
+end
+
diff --git a/test/adapter/null_test.rb b/test/adapter/null_test.rb
new file mode 100644
index 00000000..9f23b778
--- /dev/null
+++ b/test/adapter/null_test.rb
@@ -0,0 +1,25 @@
+require 'test_helper'
+
+module ActiveModel
+  class Serializer
+    class Adapter
+      class NullTest < Minitest::Test
+        def setup
+          profile = Profile.new({ name: 'Name 1', description: 'Description 1', comments: 'Comments 1' })
+          serializer = ProfileSerializer.new(profile)
+
+          @adapter = Null.new(serializer)
+        end
+
+        def test_serializable_hash
+          assert_equal({}, @adapter.serializable_hash)
+        end
+
+        def test_it_returns_empty_json
+          assert_equal('{}', @adapter.to_json)
+        end
+      end
+    end
+  end
+end
+
diff --git a/test/adapter_test.rb b/test/adapter_test.rb
new file mode 100644
index 00000000..737e0c4e
--- /dev/null
+++ b/test/adapter_test.rb
@@ -0,0 +1,23 @@
+require 'test_helper'
+
+module ActiveModel
+  class Serializer
+    class AdapterTest < Minitest::Test
+      def setup
+        profile = Profile.new
+        @serializer = ProfileSerializer.new(profile)
+        @adapter = ActiveModel::Serializer::Adapter.new(@serializer)
+      end
+
+      def test_serializable_hash_is_abstract_method
+        assert_raises(NotImplementedError) do
+          @adapter.serializable_hash(only: [:name])
+        end
+      end
+
+      def test_serializer
+        assert_equal @serializer, @adapter.serializer
+      end
+    end
+  end
+end
diff --git a/test/adapters/null_adapter_test.rb b/test/adapters/null_adapter_test.rb
deleted file mode 100644
index b50e9e12..00000000
--- a/test/adapters/null_adapter_test.rb
+++ /dev/null
@@ -1,24 +0,0 @@
-require 'test_helper'
-
-module ActiveModel
-  class Serializer
-    class Adapter
-      class NullAdapterTest < Minitest::Test
-        def setup
-          @profile = Profile.new({ name: 'Name 1', description: 'Description 1', comments: 'Comments 1' })
-          @profile_serializer = ProfileSerializer.new(@profile)
-
-          @adapter = NullAdapter.new(@profile_serializer)
-        end
-
-        def test_null_adapter
-          assert_equal('{"name":"Name 1","description":"Description 1"}',
-                       @adapter.to_json)
-
-JSON
-        end
-      end
-    end
-  end
-end
-
diff --git a/test/array_serializer_test.rb b/test/array_serializer_test.rb
new file mode 100644
index 00000000..66840a4a
--- /dev/null
+++ b/test/array_serializer_test.rb
@@ -0,0 +1,27 @@
+require 'test_helper'
+
+module ActiveModel
+  class Serializer
+    class ArraySerializerTest < Minitest::Test
+      def setup
+        @comment = Comment.new
+        @post= Post.new
+        @serializer = ArraySerializer.new([@comment, @post])
+      end
+
+      def test_respond_to_each
+        assert_respond_to @serializer, :each
+      end
+
+      def test_each_object_should_be_serializer_with_appropriate_serializer
+        serializers =  @serializer.to_a
+
+        assert_kind_of CommentSerializer, serializers.first
+        assert_kind_of Comment, serializers.first.object
+
+        assert_kind_of PostSerializer, serializers.last
+        assert_kind_of Post, serializers.last.object
+      end
+    end
+  end
+end
diff --git a/test/fixtures/poro.rb b/test/fixtures/poro.rb
index 00594811..8359fcb7 100644
--- a/test/fixtures/poro.rb
+++ b/test/fixtures/poro.rb
@@ -5,11 +5,25 @@ class Model
 
   def read_attribute_for_serialization(name)
     if name == :id || name == 'id'
-      object_id
+      id
     else
       @attributes[name]
     end
   end
+
+  def id
+    @attributes[:id] || @attributes['id'] || object_id
+  end
+
+  def method_missing(meth, *args)
+    if meth.to_s =~ /^(.*)=$/
+      @attributes[$1.to_sym] = args[0]
+    elsif @attributes.key?(meth)
+      @attributes[meth]
+    else
+      super
+    end
+  end
 end
 
 class Profile < Model
@@ -18,3 +32,18 @@ end
 class ProfileSerializer < ActiveModel::Serializer
   attributes :name, :description
 end
+
+Post = Class.new(Model)
+Comment = Class.new(Model)
+
+PostSerializer = Class.new(ActiveModel::Serializer) do
+  attributes :title, :body, :id
+
+  has_many :comments
+end
+
+CommentSerializer = Class.new(ActiveModel::Serializer) do
+  attributes :id, :body
+
+  belongs_to :post
+end
diff --git a/test/serializers/adapter_for_test.rb b/test/serializers/adapter_for_test.rb
new file mode 100644
index 00000000..60641080
--- /dev/null
+++ b/test/serializers/adapter_for_test.rb
@@ -0,0 +1,50 @@
+module ActiveModel
+  class Serializer
+    class AdapterForTest < Minitest::Test
+      def setup
+        @previous_adapter = ActiveModel::Serializer.config.adapter
+      end
+
+      def teardown
+        ActiveModel::Serializer.config.adapter = @previous_adapter
+      end
+
+      def test_returns_default_adapter
+        adapter = ActiveModel::Serializer.adapter
+        assert_equal ActiveModel::Serializer::Adapter::Json, adapter
+      end
+
+      def test_overwrite_adapter_with_symbol
+        ActiveModel::Serializer.config.adapter = :null
+
+        adapter = ActiveModel::Serializer.adapter
+        assert_equal ActiveModel::Serializer::Adapter::Null, adapter
+      ensure
+
+      end
+
+      def test_overwrite_adapter_with_class
+        ActiveModel::Serializer.config.adapter = ActiveModel::Serializer::Adapter::Null
+
+        adapter = ActiveModel::Serializer.adapter
+        assert_equal ActiveModel::Serializer::Adapter::Null, adapter
+      end
+
+      def test_raises_exception_if_invalid_symbol_given
+        ActiveModel::Serializer.config.adapter = :unknown
+
+        assert_raises ArgumentError do
+          ActiveModel::Serializer.adapter
+        end
+      end
+
+      def test_raises_exception_if_it_does_not_know_hot_to_infer_adapter
+        ActiveModel::Serializer.config.adapter = 42
+
+        assert_raises ArgumentError do
+          ActiveModel::Serializer.adapter
+        end
+      end
+    end
+  end
+end
diff --git a/test/serializers/associations_test.rb b/test/serializers/associations_test.rb
index e019c073..6d69b563 100644
--- a/test/serializers/associations_test.rb
+++ b/test/serializers/associations_test.rb
@@ -3,10 +3,6 @@ require 'test_helper'
 module ActiveModel
   class Serializer
     class AssocationsTest < Minitest::Test
-      def def_serializer(&block)
-        Class.new(ActiveModel::Serializer, &block)
-      end
-
       class Model
         def initialize(hash={})
           @attributes = hash
@@ -27,38 +23,33 @@ module ActiveModel
         end
       end
 
+
       def setup
-        @post = Model.new({ title: 'New Post', body: 'Body' })
-        @comment = Model.new({ id: 1, body: 'ZOMG A COMMENT' })
+        @post = Post.new({ title: 'New Post', body: 'Body' })
+        @comment = Comment.new({ id: 1, body: 'ZOMG A COMMENT' })
         @post.comments = [@comment]
         @comment.post = @post
 
-        @post_serializer_class = def_serializer do
-          attributes :title, :body
-        end
-
-        @comment_serializer_class = def_serializer do
-          attributes :id, :body
-        end
-
-        @post_serializer = @post_serializer_class.new(@post)
-        @comment_serializer = @comment_serializer_class.new(@comment)
+        @post_serializer = PostSerializer.new(@post)
+        @comment_serializer = CommentSerializer.new(@comment)
       end
 
       def test_has_many
-        @post_serializer_class.class_eval do
-          has_many :comments
-        end
-
         assert_equal({comments: {type: :has_many, options: {}}}, @post_serializer.class._associations)
+        @post_serializer.each_association do |name, serializer, options|
+          assert_equal(:comments, name)
+          assert_equal({}, options)
+          assert_kind_of(ActiveModel::Serializer.config.array_serializer, serializer)
+        end
       end
 
       def test_has_one
-        @comment_serializer_class.class_eval do
-          belongs_to :post
-        end
-
         assert_equal({post: {type: :belongs_to, options: {}}}, @comment_serializer.class._associations)
+        @comment_serializer.each_association do |name, serializer, options|
+          assert_equal(:post, name)
+          assert_equal({}, options)
+          assert_kind_of(PostSerializer, serializer)
+        end
       end
     end
   end
diff --git a/test/serializers/configuration_test.rb b/test/serializers/configuration_test.rb
index 91110229..eec00436 100644
--- a/test/serializers/configuration_test.rb
+++ b/test/serializers/configuration_test.rb
@@ -6,6 +6,10 @@ module ActiveModel
       def test_array_serializer
         assert_equal ActiveModel::Serializer::ArraySerializer, ActiveModel::Serializer.config.array_serializer
       end
+
+      def test_adapter
+        assert_equal :json, ActiveModel::Serializer.config.adapter
+      end
     end
   end
 end
diff --git a/test/test_helper.rb b/test/test_helper.rb
index b7875f75..bd41fb6a 100644
--- a/test/test_helper.rb
+++ b/test/test_helper.rb
@@ -27,3 +27,7 @@ ActionController::TestCase.class_eval do
     @routes = TestHelper::Routes
   end
 end
+
+def def_serializer(&block)
+  Class.new(ActiveModel::Serializer, &block)
+end