diff --git a/docs/hooks/hook_civicrm_activeThemes.md b/docs/hooks/hook_civicrm_activeThemes.md
new file mode 100644
index 0000000000000000000000000000000000000000..676a277f96cf1a002a8c7bb6d32e3393cd445bcf
--- /dev/null
+++ b/docs/hooks/hook_civicrm_activeThemes.md
@@ -0,0 +1,39 @@
+# hook_civicrm_activeTheme
+
+## Summary
+
+The activeTheme hook determines which theme is active.
+
+## Definition
+
+ hook_civicrm_activeTheme( &$theme, $context)
+
+## Parameters
+
+ - parameter string $theme
+ The identifier for the theme. Alterable.
+ Ex: 'greenwich'.
+ - parameter array $context
+ Information about the current page-request. Includes some mix of:
+ - page: the relative path of the current Civi page (Ex: 'civicrm/dashboard').
+ - themes: an instance of the Civi\Core\Themes service.
+
+## Returns
+
+- null
+
+## Availability
+
+- This hook was first available in CiviCRM 5.16
+
+## Example
+
+```php
+ /*
+ * Set which theme is active.
+ */
+
+ function civitest_civicrm_activeTheme( &$theme, $context ) {
+ $theme = 'civielection';
+ }
+```
diff --git a/docs/hooks/hook_civicrm_themes.md b/docs/hooks/hook_civicrm_themes.md
new file mode 100644
index 0000000000000000000000000000000000000000..7f6a74d1749cef5aabaf5c937cd614e5c4e25033
--- /dev/null
+++ b/docs/hooks/hook_civicrm_themes.md
@@ -0,0 +1,79 @@
+# hook_civicrm_themes
+
+## Summary
+
+This hook is called when building a list of available themes for use within CiviCRM.
+
+## Definition
+
+ hook_civicrm_themes( &$themes )
+
+## Parameters
+
+- array $themes - array of theme information
+ - ext: string (required)
+ The full name of the extension which defines the theme.
+ Ex: "org.civicrm.themes.greenwich".
+ - title: string (required)
+ Visible title.
+ - help: string (optional)
+ Description of the theme's appearance.
+ - url_callback: mixed (optional)
+ A function ($themes, $themeKey, $cssExt, $cssFile) which returns the URL(s) for a CSS resource.
+ Returns either an array of URLs or PASSTHRU.
+ Ex: \Civi\Core\Themes\Resolvers::simple (default)
+ Ex: \Civi\Core\Themes\Resolvers::none
+ - prefix: string (optional)
+ A prefix within the extension folder to prepend to the file name.
+ - search_order: array (optional)
+ A list of themes to search.
+ Generally, the last theme should be "*fallback*" (Civi\Core\Themes::FALLBACK).
+ - excludes: array (optional)
+ A list of files (eg "civicrm:css/bootstrap.css" or "$ext:$file") which should never
+ be returned (they are excluded from display). - object being imported (for now Contact
+
+## Returns
+
+- null
+
+## Availability
+
+- This hook was first available in CiviCRM 5.16
+
+## Example
+
+A minimal example:
+
+```php
+ /*
+ * A theme is a set of CSS files which are loaded on CiviCRM pages.
+ */
+ function civitest_civicrm_themes( &$themes ) {
+ $themes['civielection'] = [
+ 'title' => 'civielection theme',
+ 'ext' => 'au.org.greens.civielection',
+ ];
+ }
+```
+
+A more detailed example
+
+```php
+ /*
+ * A theme is a set of CSS files which are loaded on CiviCRM pages.
+ */
+ function civitest_civicrm_themes( &$themes ) {
+ $themes['civielection'] = [
+ 'title' => 'civielection theme',
+ 'ext' => 'au.org.greens.civielection',
+ 'name' => 'civielection',
+ 'url_callback' => '\\Civi\\Core\\Themes\\Resolvers::simple',
+ 'search_order' => [
+ 0 => 'civielection',
+ 1 => Civi\Core\Themes::FALLBACK,
+ ],
+ 'prefix' => 'election',
+ 'excludes' => ['bootstrap.css'],
+ ];
+ }
+```
diff --git a/docs/hooks/list.md b/docs/hooks/list.md
index 4d3b49d6f2003399a334dd98dd81386c57e0133a..1f0a797f9f8fc06b9712b2513fbfdce5944dee94 100644
--- a/docs/hooks/list.md
+++ b/docs/hooks/list.md
@@ -68,6 +68,7 @@ This is an overview list of all available hooks, listed by category.
## GUI Hooks
+* **[hook_civicrm_activeThemes](/hooks/hook_civicrm_activeThemes.md)** - The activeTheme hook determines which theme is active.
* **[hook_civicrm_alterEntityRefParams](/hooks/hook_civicrm_alterEntityRefParams.md)** - called when an `entityRef` field is rendered in a form, which allows you to modify the parameters used to fetch options for this kind of field.
* **[hook_civicrm_alterMenu](/hooks/hook_civicrm_alterMenu.md)** - called when building CiviCRM's list of HTTP routes and should be used when you want to register custom paths or URLS.
* **[hook_civicrm_buildAmount](/hooks/hook_civicrm_buildAmount.md)** - called when building the amount structure for a Contribution or Event Page, allowing you to modify the set of radio buttons representing amounts for contribution levels and event registration fees.
@@ -84,6 +85,7 @@ This is an overview list of all available hooks, listed by category.
* **[hook_civicrm_searchTasks](/hooks/hook_civicrm_searchTasks.md)** - called to display the list of actions allowed after doing a search, allowing you to inject additional actions or to remove existing actions.
* **[hook_civicrm_summary](/hooks/hook_civicrm_summary.md)** - called when the contact summary is rendered, allowing you to modify the summary with your own content.
* **[hook_civicrm_summaryActions](/hooks/hook_civicrm_summaryActions.md)** - allows you to customize the context menu actions on the Contact Summary Page.
+* **[hook_civicrm_themes](/hooks/hook_civicrm_themes.md)** - This Hook is called when building a list of available themes for use within CiviCRM.
* **[<del>hook_civicrm_tabs</del>](/hooks/hook_civicrm_tabs.md)** - deprecated in 4.7 in favor of [hook_civicrm_tabset](/hooks/hook_civicrm_tabset.md).
* **[hook_civicrm_tabset](/hooks/hook_civicrm_tabset.md)** - called when composing the tabs interface used for contacts, contributions and events.
* **[hook_civicrm_xmlMenu](/hooks/hook_civicrm_xmlMenu.md)** - called when building CiviCRM's menu structure, which is used to render urls in CiviCRM.
diff --git a/mkdocs.yml b/mkdocs.yml
index 5c3f00d790c3c7142781f88698ee44e108aa0806..0edf6b39e3d0b101d9f8b35c2f6c55d06d01b0fa 100644
--- a/mkdocs.yml
+++ b/mkdocs.yml
@@ -107,6 +107,7 @@ pages:
- <del>hook_civicrm_validate</del>: hooks/hook_civicrm_validate.md
- hook_civicrm_validateForm: hooks/hook_civicrm_validateForm.md
- GUI Hooks:
+ - hook_civicrm_activeThemes: hooks/hook_civicrm_activeThemes.md
- hook_civicrm_alterEntityRefParams: hooks/hook_civicrm_alterEntityRefParams.md
- hook_civicrm_alterMenu: hooks/hook_civicrm_alterMenu.md
- hook_civicrm_buildAmount: hooks/hook_civicrm_buildAmount.md
@@ -123,6 +124,7 @@ pages:
- hook_civicrm_searchTasks: hooks/hook_civicrm_searchTasks.md
- hook_civicrm_summary: hooks/hook_civicrm_summary.md
- hook_civicrm_summaryActions: hooks/hook_civicrm_summaryActions.md
+ - hook_civicrm_themes: hooks/hook_civicrm_themes.md
- <del>hook_civicrm_tabs</del>: hooks/hook_civicrm_tabs.md
- hook_civicrm_tabset: hooks/hook_civicrm_tabset.md
- hook_civicrm_xmlMenu: hooks/hook_civicrm_xmlMenu.md