diff --git a/lib/active_model/serializer.rb b/lib/active_model/serializer.rb
index 418f10ba..c267e5f0 100644
--- a/lib/active_model/serializer.rb
+++ b/lib/active_model/serializer.rb
@@ -3,16 +3,18 @@ require 'thread_safe'
 module ActiveModel
   class Serializer
     extend ActiveSupport::Autoload
+
     autoload :Configuration
     autoload :ArraySerializer
     autoload :Adapter
     autoload :Lint
+    autoload :Associations
     include Configuration
+    include Associations
 
     class << self
       attr_accessor :_attributes
       attr_accessor :_attributes_keys
-      attr_accessor :_associations
       attr_accessor :_urls
       attr_accessor :_cache
       attr_accessor :_fragmented
@@ -24,12 +26,12 @@ module ActiveModel
     end
 
     def self.inherited(base)
-      base._attributes = self._attributes.try(:dup)  || []
+      base._attributes = self._attributes.try(:dup) || []
       base._attributes_keys = self._attributes_keys.try(:dup) || {}
-      base._associations = self._associations.try(:dup) || {}
       base._urls = []
       serializer_file = File.open(caller.first[/^[^:]+/])
       base._cache_digest = Digest::MD5.hexdigest(serializer_file.read)
+      super
     end
 
     def self.attributes(*attrs)
@@ -46,7 +48,7 @@ module ActiveModel
 
     def self.attribute(attr, options = {})
       key = options.fetch(:key, attr)
-      @_attributes_keys[attr] = {key: key} if key != attr
+      @_attributes_keys[attr] = { key: key } if key != attr
       @_attributes << key unless @_attributes.include?(key)
       define_method key do
         object.read_attribute_for_serialization(attr)
@@ -59,58 +61,13 @@ module ActiveModel
 
     # Enables a serializer to be automatically cached
     def self.cache(options = {})
-      @_cache         = ActionController::Base.cache_store if Rails.configuration.action_controller.perform_caching
-      @_cache_key     = options.delete(:key)
-      @_cache_only    = options.delete(:only)
-      @_cache_except  = options.delete(:except)
+      @_cache = ActionController::Base.cache_store if Rails.configuration.action_controller.perform_caching
+      @_cache_key = options.delete(:key)
+      @_cache_only = options.delete(:only)
+      @_cache_except = options.delete(:except)
       @_cache_options = (options.empty?) ? nil : options
     end
 
-    # Defines an association in the object should be rendered.
-    #
-    # The serializer object should implement the association name
-    # as a method which should return an array when invoked. If a method
-    # with the association name does not exist, the association name is
-    # dispatched to the serialized object.
-    def self.has_many(*attrs)
-      associate(:has_many, attrs)
-    end
-
-    # Defines an association in the object that should be rendered.
-    #
-    # The serializer object should implement the association name
-    # as a method which should return an object when invoked. If a method
-    # with the association name does not exist, the association name is
-    # dispatched to the serialized object.
-    def self.belongs_to(*attrs)
-      associate(:belongs_to, attrs)
-    end
-
-    # Defines an association in the object should be rendered.
-    #
-    # The serializer object should implement the association name
-    # as a method which should return an object when invoked. If a method
-    # with the association name does not exist, the association name is
-    # dispatched to the serialized object.
-    def self.has_one(*attrs)
-      associate(:has_one, attrs)
-    end
-
-    def self.associate(type, attrs) #:nodoc:
-      options = attrs.extract_options!
-      self._associations = _associations.dup
-
-      attrs.each do |attr|
-        unless method_defined?(attr)
-          define_method attr do
-            object.send attr
-          end
-        end
-
-        self._associations[attr] = {type: type, association_options: options}
-      end
-    end
-
     def self.url(attr)
       @_urls.push attr
     end
@@ -125,19 +82,17 @@ module ActiveModel
       elsif resource.respond_to?(:to_ary)
         config.array_serializer
       else
-        options
-          .fetch(:association_options, {})
-          .fetch(:serializer, get_serializer_for(resource.class))
+        options.fetch(:serializer, get_serializer_for(resource.class))
       end
     end
 
     def self.adapter
       adapter_class = case config.adapter
-      when Symbol
-        ActiveModel::Serializer::Adapter.adapter_class(config.adapter)
-      when Class
-        config.adapter
-      end
+                      when Symbol
+                        ActiveModel::Serializer::Adapter.adapter_class(config.adapter)
+                      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}"
@@ -153,12 +108,12 @@ module ActiveModel
     attr_accessor :object, :root, :meta, :meta_key, :scope
 
     def initialize(object, options = {})
-      @object     = object
-      @options    = options
-      @root       = options[:root]
-      @meta       = options[:meta]
-      @meta_key   = options[:meta_key]
-      @scope      = options[:scope]
+      @object = object
+      @options = options
+      @root = options[:root]
+      @meta = options[:meta]
+      @meta_key = options[:meta_key]
+      @scope = options[:scope]
 
       scope_name = options[:scope_name]
       if scope_name && !respond_to?(scope_name)
@@ -199,48 +154,10 @@ module ActiveModel
       end
     end
 
-    def each_association(&block)
-      self.class._associations.dup.each do |name, association_options|
-        next unless object
-        association_value = send(name)
-
-        serializer_class = ActiveModel::Serializer.serializer_for(association_value, association_options)
-
-        if serializer_class
-          begin
-            serializer = serializer_class.new(
-              association_value,
-              options.except(:serializer).merge(serializer_from_options(association_options))
-            )
-          rescue ActiveModel::Serializer::ArraySerializer::NoSerializerError
-            virtual_value = association_value
-            virtual_value = virtual_value.as_json if virtual_value.respond_to?(:as_json)
-            association_options[:association_options][:virtual_value] = virtual_value
-          end
-        elsif !association_value.nil? && !association_value.instance_of?(Object)
-          association_options[:association_options][:virtual_value] = association_value
-        end
-
-        association_key = association_options[:association_options][:key] || name
-        if block_given?
-          block.call(association_key, serializer, association_options[:association_options])
-        end
-      end
-    end
-
-    def serializer_from_options(options)
-      opts = {}
-      serializer = options.fetch(:association_options, {}).fetch(:serializer, nil)
-      opts[:serializer] = serializer if serializer
-      opts
-    end
-
     def self.serializers_cache
       @serializers_cache ||= ThreadSafe::Cache.new
     end
 
-    private
-
     attr_reader :options
 
     def self.get_serializer_for(klass)
@@ -255,6 +172,5 @@ module ActiveModel
         end
       end
     end
-
   end
 end
diff --git a/lib/active_model/serializer/adapter/json.rb b/lib/active_model/serializer/adapter/json.rb
index 271c6959..58704b56 100644
--- a/lib/active_model/serializer/adapter/json.rb
+++ b/lib/active_model/serializer/adapter/json.rb
@@ -7,7 +7,7 @@ module ActiveModel
         def serializable_hash(options = nil)
           options ||= {}
           if serializer.respond_to?(:each)
-            @result = serializer.map{|s| FlattenJson.new(s).serializable_hash(options) }
+            @result = serializer.map { |s| FlattenJson.new(s).serializable_hash(options) }
           else
             @hash = {}
 
@@ -15,24 +15,26 @@ module ActiveModel
               serializer.attributes(options)
             end
 
-            serializer.each_association do |key, association, opts|
-              if association.respond_to?(:each)
-                array_serializer = association
-                @hash[key] = array_serializer.map do |item|
+            serializer.associations.each do |association|
+              serializer = association.serializer
+              opts = association.options
+
+              if serializer.respond_to?(:each)
+                array_serializer = serializer
+                @hash[association.key] = array_serializer.map do |item|
                   cache_check(item) do
                     item.attributes(opts)
                   end
                 end
               else
-                if association && association.object
-                  @hash[key] = cache_check(association) do
-                    association.attributes(options)
+                @hash[association.key] =
+                  if serializer && serializer.object
+                    cache_check(serializer) do
+                      serializer.attributes(options)
+                    end
+                  elsif opts[:virtual_value]
+                    opts[:virtual_value]
                   end
-                elsif opts[:virtual_value]
-                  @hash[key] = opts[:virtual_value]
-                else
-                  @hash[key] = nil
-                end
               end
             end
             @result = @core.merge @hash
diff --git a/lib/active_model/serializer/adapter/json_api.rb b/lib/active_model/serializer/adapter/json_api.rb
index 50dfb7eb..551ed54b 100644
--- a/lib/active_model/serializer/adapter/json_api.rb
+++ b/lib/active_model/serializer/adapter/json_api.rb
@@ -75,8 +75,10 @@ module ActiveModel
           end
 
           serializers.each do |serializer|
-            serializer.each_association do |key, association, opts|
-              add_included(key, association, resource_path) if association
+            serializer.associations.each do |association|
+              serializer = association.serializer
+
+              add_included(association.key, serializer, resource_path) if serializer
             end if include_nested_assoc? resource_path
           end
         end
@@ -131,22 +133,26 @@ module ActiveModel
         def add_resource_relationships(attrs, serializer, options = {})
           options[:add_included] = options.fetch(:add_included, true)
 
-          serializer.each_association do |key, association, opts|
+          serializer.associations.each do |association|
+            key = association.key
+            serializer = association.serializer
+            opts = association.options
+
             attrs[:relationships] ||= {}
 
-            if association.respond_to?(:each)
-              add_relationships(attrs, key, association)
+            if serializer.respond_to?(:each)
+              add_relationships(attrs, key, serializer)
             else
               if opts[:virtual_value]
                 add_relationship(attrs, key, nil, opts[:virtual_value])
               else
-                add_relationship(attrs, key, association)
+                add_relationship(attrs, key, serializer)
               end
             end
 
             if options[:add_included]
-              Array(association).each do |association|
-                add_included(key, association)
+              Array(serializer).each do |serializer|
+                add_included(key, serializer)
               end
             end
           end
diff --git a/lib/active_model/serializer/association.rb b/lib/active_model/serializer/association.rb
new file mode 100644
index 00000000..af1cb914
--- /dev/null
+++ b/lib/active_model/serializer/association.rb
@@ -0,0 +1,21 @@
+module ActiveModel
+  class Serializer
+    # This class hold all information about serializer's association.
+    #
+    # @param [Symbol] name
+    # @param [ActiveModel::Serializer] serializer
+    # @param [Hash{Symbol => Object}] options
+    #
+    # @example
+    #  Association.new(:comments, CommentSummarySerializer, embed: :ids)
+    #
+    Association = Struct.new(:name, :serializer, :options) do
+
+      # @return [Symbol]
+      #
+      def key
+        options.fetch(:key, name)
+      end
+    end
+  end
+end
diff --git a/lib/active_model/serializer/associations.rb b/lib/active_model/serializer/associations.rb
new file mode 100644
index 00000000..a41358c6
--- /dev/null
+++ b/lib/active_model/serializer/associations.rb
@@ -0,0 +1,107 @@
+module ActiveModel
+  class Serializer
+    # Defines an association in the object should be rendered.
+    #
+    # The serializer object should implement the association name
+    # as a method which should return an array when invoked. If a method
+    # with the association name does not exist, the association name is
+    # dispatched to the serialized object.
+    #
+    module Associations
+      extend ActiveSupport::Concern
+
+      included do |base|
+        class << base
+          attr_accessor :_reflections
+        end
+
+        autoload :Association
+        autoload :Reflection
+        autoload :SingularReflection
+        autoload :CollectionReflection
+        autoload :BelongsToReflection
+        autoload :HasOneReflection
+        autoload :HasManyReflection
+      end
+
+      module ClassMethods
+        def inherited(base)
+          base._reflections = self._reflections.try(:dup) || []
+        end
+
+        # @param [Array(Array<Symbol>, Hash{Symbol => Object})] attrs
+        # @return [void]
+        #
+        # @example
+        #  has_many :comments, serializer: CommentSummarySerializer
+        #  has_many :commits, authors
+        #
+        def has_many(*attrs)
+          associate attrs do |name, options|
+            HasManyReflection.new(name, options)
+          end
+        end
+
+        # @param [Array(Array<Symbol>, Hash{Symbol => Object})] attrs
+        # @return [void]
+        #
+        # @example
+        #  belongs_to :author, serializer: AuthorSerializer
+        #
+        def belongs_to(*attrs)
+          associate attrs do |name, options|
+            BelongsToReflection.new(name, options)
+          end
+        end
+
+        # @param [Array(Array<Symbol>, Hash{Symbol => Object})] attrs
+        # @return [void]
+        #
+        # @example
+        #  has_one :author, serializer: AuthorSerializer
+        #
+        def has_one(*attrs)
+          associate attrs do |name, options|
+            HasOneReflection.new(name, options)
+          end
+        end
+
+        private
+
+        # Add reflection and define {name} accessor.
+        # @param [Array<Symbol>]
+        # @yield [Symbol] return reflection
+        #
+        # @api private
+        #
+        def associate(attrs)
+          options = attrs.extract_options!
+
+          self._reflections = _reflections.dup
+
+          attrs.each do |name|
+            unless method_defined?(name)
+              define_method name do
+                object.send name
+              end
+            end
+
+            self._reflections << yield(name, options)
+          end
+        end
+      end
+
+      # @return [Enumerator<Association>]
+      #
+      def associations
+        return unless object
+
+        Enumerator.new do |y|
+          self.class._reflections.each do |reflection|
+            y.yield reflection.build_association(self, options)
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/lib/active_model/serializer/belongs_to_reflection.rb b/lib/active_model/serializer/belongs_to_reflection.rb
new file mode 100644
index 00000000..8cc5a201
--- /dev/null
+++ b/lib/active_model/serializer/belongs_to_reflection.rb
@@ -0,0 +1,10 @@
+module ActiveModel
+  class Serializer
+    # @api private
+    class BelongsToReflection < SingularReflection
+      def macro
+        :belongs_to
+      end
+    end
+  end
+end
diff --git a/lib/active_model/serializer/collection_reflection.rb b/lib/active_model/serializer/collection_reflection.rb
new file mode 100644
index 00000000..3436becf
--- /dev/null
+++ b/lib/active_model/serializer/collection_reflection.rb
@@ -0,0 +1,7 @@
+module ActiveModel
+  class Serializer
+    # @api private
+    class CollectionReflection < Reflection
+    end
+  end
+end
diff --git a/lib/active_model/serializer/has_many_reflection.rb b/lib/active_model/serializer/has_many_reflection.rb
new file mode 100644
index 00000000..08be4417
--- /dev/null
+++ b/lib/active_model/serializer/has_many_reflection.rb
@@ -0,0 +1,10 @@
+module ActiveModel
+  class Serializer
+    # @api private
+    class HasManyReflection < CollectionReflection
+      def macro
+        :has_many
+      end
+    end
+  end
+end
diff --git a/lib/active_model/serializer/has_one_reflection.rb b/lib/active_model/serializer/has_one_reflection.rb
new file mode 100644
index 00000000..5a915f7f
--- /dev/null
+++ b/lib/active_model/serializer/has_one_reflection.rb
@@ -0,0 +1,10 @@
+module ActiveModel
+  class Serializer
+    # @api private
+    class HasOneReflection < SingularReflection
+      def macro
+        :has_one
+      end
+    end
+  end
+end
diff --git a/lib/active_model/serializer/reflection.rb b/lib/active_model/serializer/reflection.rb
new file mode 100644
index 00000000..d9dbd670
--- /dev/null
+++ b/lib/active_model/serializer/reflection.rb
@@ -0,0 +1,74 @@
+module ActiveModel
+  class Serializer
+    # Holds all the meta-data about an association as it was specified in the
+    # ActiveModel::Serializer class.
+    #
+    # @example
+    #  class PostSerializer < ActiveModel::Serializer
+    #     has_one :author, serializer: AuthorSerializer
+    #     has_many :comments
+    #  end
+    #
+    #  PostSerializer._reflections #=>
+    #    # [
+    #    #   HasOneReflection.new(:author, serializer: AuthorSerializer),
+    #    #   HasManyReflection.new(:comments)
+    #    # ]
+    #
+    # So you can inspect reflections in your Adapters.
+    #
+    Reflection = Struct.new(:name, :options) do
+      # Build association. This method is used internally to
+      # build serializer's association by its reflection.
+      #
+      # @param [Serializer] subject is a parent serializer for given association
+      # @param [Hash{Symbol => Object}] parent_serializer_options
+      #
+      # @example
+      #    # Given the following serializer defined:
+      #    class PostSerializer < ActiveModel::Serializer
+      #      has_many :comments, serializer: CommentSummarySerializer
+      #    end
+      #
+      #    # Then you instantiate your serializer
+      #    post_serializer = PostSerializer.new(post, foo: 'bar') #
+      #    # to build association for comments you need to get reflection
+      #    comments_reflection = PostSerializer._reflections.detect { |r| r.name == :comments }
+      #    # and #build_association
+      #    comments_reflection.build_association(post_serializer, foo: 'bar')
+      #
+      # @api private
+      #
+      def build_association(subject, parent_serializer_options)
+        association_value = subject.send(name)
+        reflection_options = options.dup
+        serializer_class = ActiveModel::Serializer.serializer_for(association_value, reflection_options)
+
+        if serializer_class
+          begin
+            serializer = serializer_class.new(
+              association_value,
+              serializer_options(parent_serializer_options, reflection_options)
+            )
+          rescue ActiveModel::Serializer::ArraySerializer::NoSerializerError
+            reflection_options[:virtual_value] = association_value.try(:as_json) || association_value
+          end
+        elsif !association_value.nil? && !association_value.instance_of?(Object)
+          reflection_options[:virtual_value] = association_value
+        end
+
+        Association.new(name, serializer, reflection_options)
+      end
+
+      private
+
+      def serializer_options(parent_serializer_options, reflection_options)
+        serializer = reflection_options.fetch(:serializer, nil)
+
+        serializer_options = parent_serializer_options.except(:serializer)
+        serializer_options[:serializer] = serializer if serializer
+        serializer_options
+      end
+    end
+  end
+end
diff --git a/lib/active_model/serializer/singular_reflection.rb b/lib/active_model/serializer/singular_reflection.rb
new file mode 100644
index 00000000..f90ecc21
--- /dev/null
+++ b/lib/active_model/serializer/singular_reflection.rb
@@ -0,0 +1,7 @@
+module ActiveModel
+  class Serializer
+    # @api private
+    class SingularReflection < Reflection
+    end
+  end
+end
diff --git a/test/serializers/association_macros_test.rb b/test/serializers/association_macros_test.rb
new file mode 100644
index 00000000..f99e1980
--- /dev/null
+++ b/test/serializers/association_macros_test.rb
@@ -0,0 +1,36 @@
+require 'test_helper'
+
+module ActiveModel
+  class Serializer
+    class AssociationMacrosTest < Minitest::Test
+      AuthorSummarySerializer = Class.new
+      class AssociationsTestSerializer < Serializer
+        belongs_to :author, serializer: AuthorSummarySerializer
+        has_many :comments, embed: :ids
+        has_one :category
+      end
+
+      def before_setup
+        @reflections = AssociationsTestSerializer._reflections
+      end
+
+      def test_has_one_defines_reflection
+        has_one_reflection = HasOneReflection.new(:category, {})
+
+        assert_includes(@reflections, has_one_reflection)
+      end
+
+      def test_has_many_defines_reflection
+        has_many_reflection = HasManyReflection.new(:comments, embed: :ids)
+
+        assert_includes(@reflections, has_many_reflection)
+      end
+
+      def test_belongs_to_defines_reflection
+        belongs_to_reflection = BelongsToReflection.new(:author, serializer: AuthorSummarySerializer)
+
+        assert_includes(@reflections, belongs_to_reflection)
+      end
+    end
+  end
+end
diff --git a/test/serializers/associations_test.rb b/test/serializers/associations_test.rb
index 735311d6..89afdcc6 100644
--- a/test/serializers/associations_test.rb
+++ b/test/serializers/associations_test.rb
@@ -45,21 +45,20 @@ module ActiveModel
       end
 
       def test_has_many_and_has_one
-        assert_equal(
-          { posts: { type: :has_many, association_options: { embed: :ids } },
-            roles: { type: :has_many, association_options: { embed: :ids } },
-            bio: { type: :has_one, association_options: {} } },
-          @author_serializer.class._associations
-        )
-        @author_serializer.each_association do |key, serializer, options|
-          if key == :posts
-            assert_equal({embed: :ids}, options)
+        @author_serializer.associations.each do |association|
+          key = association.key
+          serializer = association.serializer
+          options = association.options
+
+          case key
+          when :posts
+            assert_equal({ embed: :ids }, options)
             assert_kind_of(ActiveModel::Serializer.config.array_serializer, serializer)
-          elsif key == :bio
+          when :bio
             assert_equal({}, options)
             assert_nil serializer
-          elsif key == :roles
-            assert_equal({embed: :ids}, options)
+          when :roles
+            assert_equal({ embed: :ids }, options)
             assert_kind_of(ActiveModel::Serializer.config.array_serializer, serializer)
           else
             flunk "Unknown association: #{key}"
@@ -68,7 +67,11 @@ module ActiveModel
       end
 
       def test_has_many_with_no_serializer
-        PostWithTagsSerializer.new(@post).each_association do |key, serializer, options|
+        PostWithTagsSerializer.new(@post).associations.each do |association|
+          key = association.key
+          serializer = association.serializer
+          options = association.options
+
           assert_equal key, :tags
           assert_equal serializer, nil
           assert_equal [{ attributes: { name: "#hashtagged" }}].to_json, options[:virtual_value].to_json
@@ -76,70 +79,67 @@ module ActiveModel
       end
 
       def test_serializer_options_are_passed_into_associations_serializers
-        @post_serializer.each_association do |key, association|
-          if key == :comments
-            assert association.first.custom_options[:custom_options]
-          end
-        end
+        association = @post_serializer
+                        .associations
+                        .detect { |association| association.key == :comments }
+
+        assert association.serializer.first.custom_options[:custom_options]
       end
 
       def test_belongs_to
-        assert_equal(
-          { post: { type: :belongs_to, association_options: {} },
-            author: { type: :belongs_to, association_options: {} } },
-          @comment_serializer.class._associations
-        )
-        @comment_serializer.each_association do |key, serializer, options|
-          if key == :post
-            assert_equal({}, options)
+        @comment_serializer.associations.each do |association|
+          key = association.key
+          serializer = association.serializer
+
+          case key
+          when :post
             assert_kind_of(PostSerializer, serializer)
-          elsif key == :author
-            assert_equal({}, options)
+          when :author
             assert_nil serializer
           else
             flunk "Unknown association: #{key}"
           end
+
+          assert_equal({}, association.options)
         end
       end
 
       def test_belongs_to_with_custom_method
-        blog_is_present = false
-
-        @post_serializer.each_association do |key, serializer, options|
-          blog_is_present = true if key == :blog
-        end
-
-        assert blog_is_present
+        assert(
+          @post_serializer.associations.any? do |association|
+            association.key == :blog
+          end
+        )
       end
 
       def test_associations_inheritance
         inherited_klass = Class.new(PostSerializer)
 
-        assert_equal(PostSerializer._associations, inherited_klass._associations)
+        assert_equal(PostSerializer._reflections, inherited_klass._reflections)
       end
 
       def test_associations_inheritance_with_new_association
         inherited_klass = Class.new(PostSerializer) do
           has_many :top_comments, serializer: CommentSerializer
         end
-        expected_associations = PostSerializer._associations.merge(
-          top_comments: {
-            type: :has_many,
-            association_options: {
-              serializer: CommentSerializer
-            }
-          }
+
+        assert(
+          PostSerializer._reflections.all? do |reflection|
+            inherited_klass._reflections.include?(reflection)
+          end
+        )
+
+        assert(
+          inherited_klass._reflections.any? do |reflection|
+            reflection.name == :top_comments
+          end
         )
-        assert_equal(inherited_klass._associations, expected_associations)
       end
 
       def test_associations_custom_keys
         serializer = PostWithCustomKeysSerializer.new(@post)
 
-        expected_association_keys = []
-        serializer.each_association do |key, serializer, options|
-          expected_association_keys << key
-        end
+        expected_association_keys = serializer.associations.map(&:key)
 
         assert expected_association_keys.include? :reviews
         assert expected_association_keys.include? :writer