diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2f90e7fb0..5f23557c0 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -23,6 +23,7 @@ Features:
   * adds support for `pagination links` at top level of JsonApi adapter [@bacarini]
   * adds extended format for `include` option to JsonApi adapter [@beauby]
   * adds support for wildcards in `include` option [@beauby]
+  * adds support for nested associations for JSON and Attributes adapters via the `include` option [@NullVoxPopuli, @beauby]
 
 Fixes:
 
diff --git a/lib/active_model/serializer/adapter/attributes.rb b/lib/active_model/serializer/adapter/attributes.rb
index 79cf58dcd..2d2da6ebb 100644
--- a/lib/active_model/serializer/adapter/attributes.rb
+++ b/lib/active_model/serializer/adapter/attributes.rb
@@ -9,40 +9,12 @@ def initialize(serializer, options = {})
 
         def serializable_hash(options = nil)
           options ||= {}
+
           if serializer.respond_to?(:each)
-            result = serializer.map { |s| Attributes.new(s, instance_options).serializable_hash(options) }
+            serializable_hash_for_collection(options)
           else
-            hash = {}
-
-            core = cache_check(serializer) do
-              serializer.attributes(options)
-            end
-
-            serializer.associations(@include_tree).each do |association|
-              serializer = association.serializer
-              association_options = association.options
-
-              if serializer.respond_to?(:each)
-                array_serializer = serializer
-                hash[association.key] = array_serializer.map do |item|
-                  cache_check(item) do
-                    item.attributes(association_options)
-                  end
-                end
-              else
-                hash[association.key] =
-                  if serializer && serializer.object
-                    cache_check(serializer) do
-                      serializer.attributes(options)
-                    end
-                  elsif association_options[:virtual_value]
-                    association_options[:virtual_value]
-                  end
-              end
-            end
-            result = core.merge hash
+            serializable_hash_for_single_resource(options)
           end
-          result
         end
 
         def fragment_cache(cached_hash, non_cached_hash)
@@ -51,10 +23,43 @@ def fragment_cache(cached_hash, non_cached_hash)
 
         private
 
+        def serializable_hash_for_collection(options)
+          serializer.map { |s| Attributes.new(s, instance_options).serializable_hash(options) }
+        end
+
+        def serializable_hash_for_single_resource(options)
+          resource = resource_object_for(options)
+          relationships = resource_relationships(options)
+          resource.merge!(relationships)
+        end
+
+        def resource_relationships(options)
+          relationships = {}
+          serializer.associations(@include_tree).each do |association|
+            relationships[association.key] = relationship_value_for(association, options)
+          end
+
+          relationships
+        end
+
+        def relationship_value_for(association, options)
+          return association.options[:virtual_value] if association.options[:virtual_value]
+          return unless association.serializer && association.serializer.object
+
+          opts = instance_options.merge(include: @include_tree[association.key])
+          Attributes.new(association.serializer, opts).serializable_hash(options)
+        end
+
         # no-op: Attributes adapter does not include meta data, because it does not support root.
         def include_meta(json)
           json
         end
+
+        def resource_object_for(options)
+          cache_check(serializer) do
+            serializer.attributes(options)
+          end
+        end
       end
     end
   end
diff --git a/lib/active_model/serializer/include_tree.rb b/lib/active_model/serializer/include_tree.rb
index 6d675e116..d4c82ef2b 100644
--- a/lib/active_model/serializer/include_tree.rb
+++ b/lib/active_model/serializer/include_tree.rb
@@ -1,16 +1,48 @@
 module ActiveModel
   class Serializer
+    # TODO: description of this class, and overview of how it's used
     class IncludeTree
       module Parsing
         module_function
 
+        # Translates a comma separated list of dot separated paths (JSON API format) into a Hash.
+        #
+        # @example
+        #   `'posts.author, posts.comments.upvotes, posts.comments.author'`
+        #
+        #   would become
+        #
+        #   `{ posts: { author: {}, comments: { author: {}, upvotes: {} } } }`.
+        #
+        # @param [String] included
+        # @return [Hash] a Hash representing the same tree structure
         def include_string_to_hash(included)
+          # TODO: Needs comment walking through the process of what all this is doing.
           included.delete(' ').split(',').reduce({}) do |hash, path|
             include_tree = path.split('.').reverse_each.reduce({}) { |a, e| { e.to_sym => a } }
             hash.deep_merge!(include_tree)
           end
         end
 
+        # Translates the arguments passed to the include option into a Hash. The format can be either
+        # a String (see #include_string_to_hash), an Array of Symbols and Hashes, or a mix of both.
+        #
+        # @example
+        #  `posts: [:author, comments: [:author, :upvotes]]`
+        #
+        #  would become
+        #
+        #   `{ posts: { author: {}, comments: { author: {}, upvotes: {} } } }`.
+        #
+        # @example
+        #  `[:author, :comments => [:author]]`
+        #
+        #   would become
+        #
+        #   `{:author => {}, :comments => { author: {} } }`
+        #
+        # @param [Symbol, Hash, Array, String] included
+        # @return [Hash] a Hash representing the same tree structure
         def include_args_to_hash(included)
           case included
           when Symbol
@@ -47,6 +79,8 @@ def self.from_string(included)
       # @return [IncludeTree]
       #
       def self.from_include_args(included)
+        return included if included.is_a?(IncludeTree)
+
         new(Parsing.include_args_to_hash(included))
       end
 
diff --git a/test/action_controller/json/include_test.rb b/test/action_controller/json/include_test.rb
new file mode 100644
index 000000000..ac5ab25e6
--- /dev/null
+++ b/test/action_controller/json/include_test.rb
@@ -0,0 +1,167 @@
+require 'test_helper'
+
+module ActionController
+  module Serialization
+    class Json
+      class IncludeTest < ActionController::TestCase
+        class IncludeTestController < ActionController::Base
+          def setup_data
+            ActionController::Base.cache_store.clear
+
+            @author = Author.new(id: 1, name: 'Steve K.')
+
+            @post = Post.new(id: 42, 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]
+            @post.author = @author
+
+            @first_comment.post = @post
+            @second_comment.post = @post
+
+            @blog = Blog.new(id: 1, name: 'My Blog!!')
+            @post.blog = @blog
+            @author.posts = [@post]
+
+            @first_comment.author = @author
+            @second_comment.author = @author
+            @author.comments = [@first_comment, @second_comment]
+            @author.roles = []
+            @author.bio = {}
+          end
+
+          def render_without_include
+            setup_data
+            render json: @author, adapter: :json
+          end
+
+          def render_resource_with_include_hash
+            setup_data
+            render json: @author, include: { posts: :comments }, adapter: :json
+          end
+
+          def render_resource_with_include_string
+            setup_data
+            render json: @author, include: 'posts.comments', adapter: :json
+          end
+
+          def render_resource_with_deep_include
+            setup_data
+            render json: @author, include: 'posts.comments.author', adapter: :json
+          end
+        end
+
+        tests IncludeTestController
+
+        def test_render_without_include
+          get :render_without_include
+          response = JSON.parse(@response.body)
+          expected = {
+            'author' => {
+              'id' => 1,
+              'name' => 'Steve K.',
+              'posts' => [
+                {
+                  'id' => 42, 'title' => 'New Post', 'body' => 'Body'
+                }
+              ],
+              'roles' => [],
+              'bio' => {}
+            }
+          }
+
+          assert_equal(expected, response)
+        end
+
+        def test_render_resource_with_include_hash
+          get :render_resource_with_include_hash
+          response = JSON.parse(@response.body)
+          expected = {
+            'author' => {
+              'id' => 1,
+              'name' => 'Steve K.',
+              'posts' => [
+                {
+                  'id' => 42, 'title' => 'New Post', 'body' => 'Body',
+                  'comments' => [
+                    {
+                      'id' => 1, 'body' => 'ZOMG A COMMENT'
+                    },
+                    {
+                      'id' => 2, 'body' => 'ZOMG ANOTHER COMMENT'
+                    }
+                  ]
+                }
+              ]
+            }
+          }
+
+          assert_equal(expected, response)
+        end
+
+        def test_render_resource_with_include_string
+          get :render_resource_with_include_string
+
+          response = JSON.parse(@response.body)
+          expected = {
+            'author' => {
+              'id' => 1,
+              'name' => 'Steve K.',
+              'posts' => [
+                {
+                  'id' => 42, 'title' => 'New Post', 'body' => 'Body',
+                  'comments' => [
+                    {
+                      'id' => 1, 'body' => 'ZOMG A COMMENT'
+                    },
+                    {
+                      'id' => 2, 'body' => 'ZOMG ANOTHER COMMENT'
+                    }
+                  ]
+                }
+              ]
+            }
+          }
+
+          assert_equal(expected, response)
+        end
+
+        def test_render_resource_with_deep_include
+          get :render_resource_with_deep_include
+
+          response = JSON.parse(@response.body)
+          expected = {
+            'author' => {
+              'id' => 1,
+              'name' => 'Steve K.',
+              'posts' => [
+                {
+                  'id' => 42, 'title' => 'New Post', 'body' => 'Body',
+                  'comments' => [
+                    {
+                      'id' => 1, 'body' => 'ZOMG A COMMENT',
+                      'author' => {
+                        'id' => 1,
+                        'name' => 'Steve K.'
+                      }
+                    },
+                    {
+                      'id' => 2, 'body' => 'ZOMG ANOTHER COMMENT',
+                      'author' => {
+                        'id' => 1,
+                        'name' => 'Steve K.'
+                      }
+                    }
+                  ]
+                }
+              ]
+            }
+          }
+
+          assert_equal(expected, response)
+        end
+      end
+    end
+  end
+end
diff --git a/test/include_tree/include_args_to_hash_test.rb b/test/include_tree/include_args_to_hash_test.rb
new file mode 100644
index 000000000..cb5d5c355
--- /dev/null
+++ b/test/include_tree/include_args_to_hash_test.rb
@@ -0,0 +1,51 @@
+require 'test_helper'
+
+module ActiveModel
+  class Serializer
+    class IncludeTree
+      module Parsing
+        class IncludeArgsToHashTest < MiniTest::Test
+          def test_include_args_to_hash_from_symbol
+            expected = { author: {} }
+            input = :author
+            actual = Parsing.include_args_to_hash(input)
+
+            assert_equal(expected, actual)
+          end
+
+          def test_include_args_to_hash_from_array
+            expected = { author: {}, comments: {} }
+            input = [:author, :comments]
+            actual = Parsing.include_args_to_hash(input)
+
+            assert_equal(expected, actual)
+          end
+
+          def test_include_args_to_hash_from_nested_array
+            expected = { author: {}, comments: { author: {} } }
+            input = [:author, comments: [:author]]
+            actual = Parsing.include_args_to_hash(input)
+
+            assert_equal(expected, actual)
+          end
+
+          def test_include_args_to_hash_from_array_of_hashes
+            expected = {
+              author: {},
+              blogs: { posts: { contributors: {} } },
+              comments: { author: { blogs: { posts: {} } } }
+            }
+            input = [
+              :author,
+              blogs: [posts: :contributors],
+              comments: { author: { blogs: :posts } }
+            ]
+            actual = Parsing.include_args_to_hash(input)
+
+            assert_equal(expected, actual)
+          end
+        end
+      end
+    end
+  end
+end