diff --git a/lib/active_model/serializer.rb b/lib/active_model/serializer.rb
index a34136c9..eadcb32e 100644
--- a/lib/active_model/serializer.rb
+++ b/lib/active_model/serializer.rb
@@ -3,6 +3,7 @@ require 'active_model/serializer/collection_serializer'
 require 'active_model/serializer/array_serializer'
 require 'active_model/serializer/include_tree'
 require 'active_model/serializer/associations'
+require 'active_model/serializer/attributes'
 require 'active_model/serializer/configuration'
 require 'active_model/serializer/fieldset'
 require 'active_model/serializer/lint'
@@ -13,6 +14,7 @@ module ActiveModel
   class Serializer
     include Configuration
     include Associations
+    include Attributes
     require 'active_model/serializer/adapter'
 
     # Matches
@@ -45,14 +47,9 @@ module ActiveModel
     end
 
     with_options instance_writer: false, instance_reader: false do |serializer|
-      class_attribute :_type, instance_reader: true
-      class_attribute :_attributes               # @api private : names of attribute methods, @see Serializer#attribute
-      self._attributes ||= []
-      class_attribute :_attributes_keys          # @api private : maps attribute value to explict key name, @see Serializer#attribute
-      self._attributes_keys ||= {}
-      class_attribute :_links                    # @api private : links definitions, @see Serializer#link
+      serializer.class_attribute :_type, instance_reader: true
+      serializer.class_attribute :_links         # @api private : links definitions, @see Serializer#link
       self._links ||= {}
-
       serializer.class_attribute :_cache         # @api private : the cache object
       serializer.class_attribute :_fragmented    # @api private : @see ::fragmented
       serializer.class_attribute :_cache_key     # @api private : when present, is first item in cache_key
@@ -69,12 +66,10 @@ module ActiveModel
       serializer.class_attribute :_cache_digest # @api private : Generated
     end
 
-    # Serializers inherit _attributes and _attributes_keys.
+    # Serializers inherit _attribute_mappings, _reflections, and _links.
     # Generates a unique digest for each serializer at load.
     def self.inherited(base)
       caller_line = caller.first
-      base._attributes = _attributes.dup
-      base._attributes_keys = _attributes_keys.dup
       base._links = _links.dup
       base._cache_digest = digest_caller_file(caller_line)
       super
@@ -91,37 +86,6 @@ module ActiveModel
       _links[name] = block || value
     end
 
-    # @example
-    #   class AdminAuthorSerializer < ActiveModel::Serializer
-    #     attributes :id, :name, :recent_edits
-    def self.attributes(*attrs)
-      attrs = attrs.first if attrs.first.class == Array
-
-      attrs.each do |attr|
-        attribute(attr)
-      end
-    end
-
-    # @example
-    #   class AdminAuthorSerializer < ActiveModel::Serializer
-    #     attributes :id, :recent_edits
-    #     attribute :name, key: :title
-    #
-    #     def recent_edits
-    #       object.edits.last(5)
-    #     enr
-    def self.attribute(attr, options = {})
-      key = options.fetch(:key, attr)
-      _attributes_keys[attr] = { key: key } if key != attr
-      _attributes << key unless _attributes.include?(key)
-
-      ActiveModelSerializers.silence_warnings do
-        define_method key do
-          object.read_attribute_for_serialization(attr)
-        end unless method_defined?(key) || _fragmented.respond_to?(attr)
-      end
-    end
-
     # @api private
     # Used by FragmentCache on the CachedSerializer
     #  to call attribute methods on the fragmented cached serializer.
@@ -220,6 +184,15 @@ module ActiveModel
       end
     end
 
+    def self._serializer_instance_method_defined?(name)
+      _serializer_instance_methods.include?(name)
+    end
+
+    def self._serializer_instance_methods
+      @_serializer_instance_methods ||= (public_instance_methods - Object.public_instance_methods).to_set
+    end
+    private_class_method :_serializer_instance_methods
+
     attr_accessor :object, :root, :scope
 
     # `scope_name` is set as :current_user by default in the controller.
@@ -244,16 +217,13 @@ module ActiveModel
       root || object.class.model_name.to_s.underscore
     end
 
-    # Return the +attributes+ of +object+ as presented
-    # by the serializer.
-    def attributes(requested_attrs = nil)
-      self.class._attributes.each_with_object({}) do |name, hash|
-        next unless requested_attrs.nil? || requested_attrs.include?(name)
-        if self.class._fragmented
-          hash[name] = self.class._fragmented.public_send(name)
-        else
-          hash[name] = send(name)
-        end
+    def read_attribute_for_serialization(attr)
+      if self.class._serializer_instance_method_defined?(attr)
+        send(attr)
+      elsif self.class._fragmented
+        self.class._fragmented.read_attribute_for_serialization(attr)
+      else
+        object.read_attribute_for_serialization(attr)
       end
     end
 
diff --git a/lib/active_model/serializer/associations.rb b/lib/active_model/serializer/associations.rb
index af627a13..c4da3515 100644
--- a/lib/active_model/serializer/associations.rb
+++ b/lib/active_model/serializer/associations.rb
@@ -12,9 +12,10 @@ module ActiveModel
 
       DEFAULT_INCLUDE_TREE = ActiveModel::Serializer::IncludeTree.from_string('*')
 
-      included do |base|
-        class << base
-          attr_accessor :_reflections
+      included do
+        with_options instance_writer: false, instance_reader: true do |serializer|
+          serializer.class_attribute :_reflections
+          self._reflections ||= []
         end
 
         extend ActiveSupport::Autoload
@@ -29,7 +30,8 @@ module ActiveModel
 
       module ClassMethods
         def inherited(base)
-          base._reflections = self._reflections.try(:dup) || []
+          super
+          base._reflections = _reflections.dup
         end
 
         # @param [Symbol] name of the association
@@ -39,8 +41,8 @@ module ActiveModel
         # @example
         #  has_many :comments, serializer: CommentSummarySerializer
         #
-        def has_many(name, options = {})
-          associate HasManyReflection.new(name, options)
+        def has_many(name, options = {}, &block)
+          associate(HasManyReflection.new(name, options, block))
         end
 
         # @param [Symbol] name of the association
@@ -50,8 +52,8 @@ module ActiveModel
         # @example
         #  belongs_to :author, serializer: AuthorSerializer
         #
-        def belongs_to(name, options = {})
-          associate BelongsToReflection.new(name, options)
+        def belongs_to(name, options = {}, &block)
+          associate(BelongsToReflection.new(name, options, block))
         end
 
         # @param [Symbol] name of the association
@@ -61,8 +63,8 @@ module ActiveModel
         # @example
         #  has_one :author, serializer: AuthorSerializer
         #
-        def has_one(name, options = {})
-          associate HasOneReflection.new(name, options)
+        def has_one(name, options = {}, &block)
+          associate(HasOneReflection.new(name, options, block))
         end
 
         private
@@ -76,10 +78,6 @@ module ActiveModel
         def associate(reflection)
           self._reflections = _reflections.dup
 
-          define_method reflection.name do
-            object.send reflection.name
-          end unless method_defined?(reflection.name)
-
           self._reflections << reflection
         end
       end
diff --git a/lib/active_model/serializer/attributes.rb b/lib/active_model/serializer/attributes.rb
new file mode 100644
index 00000000..81f6e49a
--- /dev/null
+++ b/lib/active_model/serializer/attributes.rb
@@ -0,0 +1,112 @@
+module ActiveModel
+  class Serializer
+    module Attributes
+      # @api private
+      class Attribute
+        delegate :call, to: :reader
+
+        attr_reader :name, :reader
+
+        def initialize(name)
+          @name = name
+          @reader = :no_reader
+        end
+
+        def self.build(name, block)
+          if block
+            AttributeBlock.new(name, block)
+          else
+            AttributeReader.new(name)
+          end
+        end
+      end
+      # @api private
+      class AttributeReader < Attribute
+        def initialize(name)
+          super(name)
+          @reader = ->(instance) { instance.read_attribute_for_serialization(name) }
+        end
+      end
+      # @api private
+      class AttributeBlock < Attribute
+        def initialize(name, block)
+          super(name)
+          @reader = ->(instance) { instance.instance_eval(&block) }
+        end
+      end
+
+      extend ActiveSupport::Concern
+
+      included do
+        with_options instance_writer: false, instance_reader: false do |serializer|
+          serializer.class_attribute :_attribute_mappings # @api private : maps attribute key names to names to names of implementing methods, @see #attribute
+          self._attribute_mappings ||= {}
+        end
+
+        # Return the +attributes+ of +object+ as presented
+        # by the serializer.
+        def attributes(requested_attrs = nil, reload = false)
+          @attributes = nil if reload
+          @attributes ||= self.class._attribute_mappings.each_with_object({}) do |(key, attribute_mapping), hash|
+            next unless requested_attrs.nil? || requested_attrs.include?(key)
+            hash[key] = attribute_mapping.call(self)
+          end
+        end
+      end
+
+      module ClassMethods
+        def inherited(base)
+          super
+          base._attribute_mappings = _attribute_mappings.dup
+        end
+
+        # @example
+        #   class AdminAuthorSerializer < ActiveModel::Serializer
+        #     attributes :id, :name, :recent_edits
+        def attributes(*attrs)
+          attrs = attrs.first if attrs.first.class == Array
+
+          attrs.each do |attr|
+            attribute(attr)
+          end
+        end
+
+        # @example
+        #   class AdminAuthorSerializer < ActiveModel::Serializer
+        #     attributes :id, :recent_edits
+        #     attribute :name, key: :title
+        #
+        #     attribute :full_name do
+        #       "#{object.first_name} #{object.last_name}"
+        #     end
+        #
+        #     def recent_edits
+        #       object.edits.last(5)
+        #     end
+        def attribute(attr, options = {}, &block)
+          key = options.fetch(:key, attr)
+          _attribute_mappings[key] = Attribute.build(attr, block)
+        end
+
+        # @api private
+        # names of attribute methods
+        # @see Serializer::attribute
+        def _attributes
+          _attribute_mappings.keys
+        end
+
+        # @api private
+        # maps attribute value to explict key name
+        # @see Serializer::attribute
+        # @see Adapter::FragmentCache#fragment_serializer
+        def _attributes_keys
+          _attribute_mappings
+            .each_with_object({}) do |(key, attribute_mapping), hash|
+              next if key == attribute_mapping.name
+              hash[attribute_mapping.name] = { key: key }
+            end
+        end
+      end
+    end
+  end
+end
diff --git a/lib/active_model/serializer/reflection.rb b/lib/active_model/serializer/reflection.rb
index 18850abe..c027d96e 100644
--- a/lib/active_model/serializer/reflection.rb
+++ b/lib/active_model/serializer/reflection.rb
@@ -7,8 +7,16 @@ module ActiveModel
     #  class PostSerializer < ActiveModel::Serializer
     #     has_one :author, serializer: AuthorSerializer
     #     has_many :comments
+    #     has_many :comments, key: :last_comments do
+    #       last(1)
+    #     end
     #  end
     #
+    #  Notice that the association block is evaluated in the context of the association.
+    #  Specifically, the association 'comments' is evaluated two different ways:
+    #  1) as 'comments' and named 'comments'.
+    #  2) as 'comments.last(1)' and named 'last_comments'.
+    #
     #  PostSerializer._reflections #=>
     #    # [
     #    #   HasOneReflection.new(:author, serializer: AuthorSerializer),
@@ -17,7 +25,30 @@ module ActiveModel
     #
     # So you can inspect reflections in your Adapters.
     #
-    Reflection = Struct.new(:name, :options) do
+    Reflection = Struct.new(:name, :options, :block) do
+      delegate :call, to: :reader
+
+      attr_reader :reader
+
+      def initialize(*)
+        super
+        @reader = self.class.build_reader(name, block)
+      end
+
+      # @api private
+      def value(instance)
+        call(instance)
+      end
+
+      # @api private
+      def self.build_reader(name, block)
+        if block
+          ->(instance) { instance.read_attribute_for_serialization(name).instance_eval(&block) }
+        else
+          ->(instance) { instance.read_attribute_for_serialization(name) }
+        end
+      end
+
       # Build association. This method is used internally to
       # build serializer's association by its reflection.
       #
@@ -40,7 +71,7 @@ module ActiveModel
       # @api private
       #
       def build_association(subject, parent_serializer_options)
-        association_value = subject.send(name)
+        association_value = value(subject)
         reflection_options = options.dup
         serializer_class = subject.class.serializer_for(association_value, reflection_options)
 
diff --git a/test/fixtures/poro.rb b/test/fixtures/poro.rb
index 573b3fa8..5a6e3681 100644
--- a/test/fixtures/poro.rb
+++ b/test/fixtures/poro.rb
@@ -116,7 +116,7 @@ RoleSerializer = Class.new(ActiveModel::Serializer) do
   attributes :id, :name, :description, :slug
 
   def slug
-    "#{name}-#{id}"
+    "#{object.name}-#{object.id}"
   end
 
   belongs_to :author
diff --git a/test/serializers/associations_test.rb b/test/serializers/associations_test.rb
index 205cfcc8..ecb671f2 100644
--- a/test/serializers/associations_test.rb
+++ b/test/serializers/associations_test.rb
@@ -126,6 +126,35 @@ module ActiveModel
         assert expected_association_keys.include? :site
       end
 
+      class InlineAssociationTestPostSerializer < ActiveModel::Serializer
+        has_many :comments
+        has_many :comments, key: :last_comments do
+          last(1)
+        end
+      end
+
+      def test_virtual_attribute_block
+        comment1 = ::ARModels::Comment.create!(contents: 'first comment')
+        comment2 = ::ARModels::Comment.create!(contents: 'last comment')
+        post = ::ARModels::Post.create!(
+          title: 'inline association test',
+          body: 'etc',
+          comments: [comment1, comment2]
+        )
+        actual = serializable(post, adapter: :attributes, serializer: InlineAssociationTestPostSerializer).as_json
+        expected = {
+          :comments =>           [
+            { :id => 1, :contents => 'first comment' },
+            { :id => 2, :contents => 'last comment' }
+          ],
+          :last_comments =>           [
+            { :id => 2, :contents => 'last comment' }
+          ]
+        }
+
+        assert_equal expected, actual
+      end
+
       class NamespacedResourcesTest < Minitest::Test
         class ResourceNamespace
           Post    = Class.new(::Model)
diff --git a/test/serializers/attribute_test.rb b/test/serializers/attribute_test.rb
index 99452e53..cf9dae4f 100644
--- a/test/serializers/attribute_test.rb
+++ b/test/serializers/attribute_test.rb
@@ -43,6 +43,15 @@ module ActiveModel
         assert_equal({ blog: { id: 'AMS Hints' } }, adapter.serializable_hash)
       end
 
+      def test_object_attribute_override
+        serializer = Class.new(ActiveModel::Serializer) do
+          attribute :name, key: :object
+        end
+
+        adapter = ActiveModel::Serializer::Adapter::Json.new(serializer.new(@blog))
+        assert_equal({ blog: { object: 'AMS Hints' } }, adapter.serializable_hash)
+      end
+
       def test_type_attribute
         attribute_serializer = Class.new(ActiveModel::Serializer) do
           attribute :id, key: :type
@@ -71,6 +80,21 @@ module ActiveModel
 
         assert_equal('custom', hash[:blog][:id])
       end
+
+      PostWithVirtualAttribute = Class.new(::Model)
+      class PostWithVirtualAttributeSerializer < ActiveModel::Serializer
+        attribute :name do
+          "#{object.first_name} #{object.last_name}"
+        end
+      end
+
+      def test_virtual_attribute_block
+        post = PostWithVirtualAttribute.new(first_name: 'Lucas', last_name: 'Hosseini')
+        hash = serializable(post).serializable_hash
+        expected = { name: 'Lucas Hosseini' }
+
+        assert_equal(expected, hash)
+      end
     end
   end
 end