diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3cd19e2..d0f9bc8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,7 @@
 
 * Your contribution here.
 
+* [#108](https://github.com/ruby-grape/grape-active_model_serializers/pull/108): Document JSON:API included resources and verify relationship linkage, explicit inclusion, and collection deduplication through API requests - [@dblock](https://github.com/dblock).
 * [#110](https://github.com/ruby-grape/grape-active_model_serializers/pull/110): Add SimpleCov LCOV reports, merged stable-matrix Coveralls reporting, and a coverage badge; remove the obsolete Code Climate badge and refresh gem/CI badge links - [@dblock](https://github.com/dblock).
 * [#109](https://github.com/ruby-grape/grape-active_model_serializers/pull/109): Document the optional third-party Swagger model parser, response model configuration, and schema limitations - [@dblock](https://github.com/dblock).
 * [#106](https://github.com/ruby-grape/grape-active_model_serializers/pull/106): Update default serializer options documentation to use AMS 0.10 field filtering and cover request-level defaults and overrides - [@dblock](https://github.com/dblock).
diff --git a/README.md b/README.md
index 2f30de4..a8ec25d 100644
--- a/README.md
+++ b/README.md
@@ -12,6 +12,7 @@
     - [API Versioning](#api-versioning)
     - [Manually specifying serializer / adapter options](#manually-specifying-serializer--adapter-options)
     - [Error Serialization](#error-serialization)
+    - [JSON:API Included Resources](#jsonapi-included-resources)
     - [Custom Metadata](#custom-metadata)
     - [Default Serializer Options](#default-serializer-options)
     - [Current User](#current-user)
@@ -257,6 +258,50 @@ end
 
 With the `:json_api` adapter, validation failures return HTTP 422 with a [JSON:API errors array](https://jsonapi.org/format/#error-objects). The response shape follows the configured ActiveModelSerializers adapter, not the Grape format name: the example still uses `format :json`. Setting the global adapter also affects successful responses.
 
+### JSON:API Included Resources
+
+A resource identifier under `relationships` is linkage, not the related resource's attributes. To include those attributes in a top-level `included` array, declare the relationship in the serializer and pass an AMS `include` option with the `:json_api` adapter:
+
+```ruby
+class AuthorSerializer < ActiveModel::Serializer
+  attributes :id, :name
+end
+
+class ArticleSerializer < ActiveModel::Serializer
+  attributes :id, :title
+  belongs_to :author, serializer: AuthorSerializer
+end
+
+get '/articles/:id' do
+  article = Article.find(params[:id])
+  render article, adapter: :json_api, include: 'author'
+end
+```
+
+With the Grape AMS formatter configured and `format :json`, an article with an author produces a compound document such as:
+
+```json
+{
+  "data": {
+    "id": "1",
+    "type": "articles",
+    "attributes": { "title": "Hello" },
+    "relationships": {
+      "author": { "data": { "id": "2", "type": "authors" } }
+    }
+  },
+  "included": [
+    { "id": "2", "type": "authors", "attributes": { "name": "Jane" } }
+  ]
+}
+```
+
+Related records need identifiers and serializers defining the attributes to expose. Without `include: 'author'`, the JSON:API adapter can emit relationship linkage without adding the author's full resource to `included`.
+
+You can also specify `adapter: :json_api, include: 'author'` as route options, or return them from `default_serializer_options`. Nested relationships use paths such as `include: 'comments.author'`; each relationship must be declared in its serializer.
+
+ActiveRecord's `includes(:author)` preloads database associations but does not select AMS included resources. Likewise, an `?include=author` query parameter is not automatically forwarded to AMS; validate allowed relationships and explicitly pass the selected include option. See the [AMS include documentation](https://github.com/rails-api/active_model_serializers/blob/0-10-stable/docs/general/adapters.md#include-option).
+
 ### Custom Metadata
 
 ```ruby
diff --git a/spec/features/grape-active_model_serializers/render_spec.rb b/spec/features/grape-active_model_serializers/render_spec.rb
index c2293c8..6eb6f87 100644
--- a/spec/features/grape-active_model_serializers/render_spec.rb
+++ b/spec/features/grape-active_model_serializers/render_spec.rb
@@ -115,3 +115,78 @@ def get_resource_with(meta)
     end
   end
 end
+
+describe 'JSON:API included resources' do
+  let(:app) { Class.new(Grape::API) }
+  let(:render_options) { { adapter: :json_api } }
+  let(:route_options) { {} }
+  let(:collection) { false }
+  let(:document) { JSON.parse(last_response.body) }
+  let(:author_resource) {
+    { 'id' => '2', 'type' => 'authors', 'attributes' => { 'name' => 'Jane' } }
+  }
+
+  before do
+    stub_const('JsonApiAuthor', Class.new(ActiveModelSerializers::Model) do
+      attributes :id, :name
+    end)
+    stub_const('JsonApiArticle', Class.new(ActiveModelSerializers::Model) do
+      attributes :id, :title, :author
+    end)
+    stub_const('JsonApiAuthorSerializer', Class.new(ActiveModel::Serializer) do
+      type 'authors'
+      attributes :id, :name
+    end)
+    stub_const('JsonApiArticleSerializer', Class.new(ActiveModel::Serializer) do
+      type 'articles'
+      attributes :id, :title
+      belongs_to :author, serializer: JsonApiAuthorSerializer
+    end)
+
+    ActiveModelSerializers.config.adapter = :json
+    app.format :json
+    app.formatter :json, Grape::Formatter::ActiveModelSerializers
+    author = JsonApiAuthor.new(id: 2, name: 'Jane')
+    article = JsonApiArticle.new(id: 1, title: 'Hello', author: author)
+    articles = [article, JsonApiArticle.new(id: 3, title: 'More', author: author)]
+    resource = collection ? articles : article
+    options = render_options
+    app.get('/articles', **route_options) { render resource, options }
+
+    get '/articles'
+  end
+
+  it 'emits relationship linkage without implicitly including the resource' do
+    expect(document.fetch('data').fetch('relationships')).to eq(
+      'author' => { 'data' => { 'id' => '2', 'type' => 'authors' } }
+    )
+    expect(document).not_to have_key('included')
+  end
+
+  context 'render inclusion' do
+    let(:render_options) { super().merge(include: 'author') }
+
+    it 'includes the related resource and its attributes' do
+      expect(document.fetch('included')).to eq([author_resource])
+    end
+
+    context 'a collection' do
+      let(:collection) { true }
+
+      it 'includes a shared related resource only once' do
+        ids = document.fetch('data').map { |article| article.fetch('id') }
+        expect(ids).to eq(%w[1 3])
+        expect(document.fetch('included')).to eq([author_resource])
+      end
+    end
+  end
+
+  context 'route options' do
+    let(:route_options) { { adapter: :json_api, include: 'author' } }
+    let(:render_options) { {} }
+
+    it 'selects the adapter and included resource without render overrides' do
+      expect(document.fetch('included')).to eq([author_resource])
+    end
+  end
+end