diff --git a/_includes/sidebar-custom.html b/_includes/sidebar-custom.html
new file mode 100644
index 000000000000..e69de29bb2d1
diff --git a/_includes/sidebar.html b/_includes/sidebar.html
index d0228f1cff4d..f701662c5123 100644
--- a/_includes/sidebar.html
+++ b/_includes/sidebar.html
@@ -16,5 +16,6 @@
       {% include nav_list locale=locale nav=page.sidebar.nav %}
     {% endif %}
   {% endif %}
+  {% include sidebar-custom.html %}
   </div>
 {% endif %}
diff --git a/docs/_docs/10-layouts.md b/docs/_docs/10-layouts.md
index a2cf7ee7df8d..9aa99d8f4a28 100644
--- a/docs/_docs/10-layouts.md
+++ b/docs/_docs/10-layouts.md
@@ -663,6 +663,8 @@ sidebar:
 **Note:** Custom sidebar content added to a post or page's YAML Front Matter will appear below the author profile if enabled with `author_profile: true`.
 {: .notice--info}
 
+For more advanced customization, create `_includes/sidebar-custom.html` in your site. Its contents are included at the bottom of the sidebar on every page, after the author profile, YAML-defined blocks, and navigation menu. This follows the same pattern as [`head/custom.html`](#custom-head-tags) and `author-profile-custom-links.html`.
+
 ### Custom sidebar navigation menu
 
 To create a sidebar menu[^sidebar-menu] similar to the one found in the theme's documentation pages you'll need to modify a `_data` file and some YAML Front Matter.