diff --git a/CHANGELOG.md b/CHANGELOG.md
index c982f21a..46df5b05 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,7 @@
+### 4.0.16 - 2018-09-10
+### Added
+- Added map_source event for mapping custom sources. See the Events section in the README for more.
+
 ## 4.0.15 - 2018-08-31
 ### Added
 - Schematic can now parse environment variables in the schema file directly, without need for an override file
diff --git a/README.md b/README.md
index 7e14b2dd..5976e0d4 100644
--- a/README.md
+++ b/README.md
@@ -133,7 +133,7 @@ Then the environment variable `KEY_VALUE` needs to be set. The value of this env
 
 Environment variables can also directly be used in the `schema.yml` file. Beware that if you do that, they will be overriden on export by their environment variable's values.
 
-### Hooks
+### Events
 
 Custom converters can be injected with the `EVENT_RESOLVE_CONVERTER` event.
 This can be especially useful for importing and exporting custom field types.
@@ -147,6 +147,22 @@ Event::on(Schematic::class, Schematic::EVENT_RESOLVE_CONVERTER, function (Conver
 });
 ```
 
+Custom source mappings can be injected with the `EVENT_MAP_SOURCE` event.
+This can be especially useful for importing and exporting custom sources.
+
+```php
+Event::on(Schematic::class, Schematic::EVENT_MAP_SOURCE, function (SourceMappingEvent $event) {
+    list($sourceType, $sourceFrom) = explode(':', $event->source);
+
+    switch ($sourceType) {
+        case 'plugin-source':
+            $event->service = Craft::$app->customService;
+            $event->method = 'getCustomModelBy';
+            break;
+    }
+});
+```
+
 ### Caveats
 
 Schematic uses handles to identify content. When a handle is changed in the schema file and import is run with force a new content type will be created with that handle, and the old content type will be deleted!
diff --git a/composer.json b/composer.json
index 9f004676..84920d02 100644
--- a/composer.json
+++ b/composer.json
@@ -1,5 +1,5 @@
 {
-    "version": "4.0.15",
+    "version": "4.0.16",
     "name": "nerds-and-company/schematic",
     "description": "Craft setup and sync tool",
     "type": "craft-plugin",
diff --git a/src/Behaviors/SourcesBehavior.php b/src/Behaviors/SourcesBehavior.php
index 4ca0b2ea..1282e035 100644
--- a/src/Behaviors/SourcesBehavior.php
+++ b/src/Behaviors/SourcesBehavior.php
@@ -7,6 +7,7 @@
 use yii\base\Behavior;
 use craft\base\Model;
 use NerdsAndCompany\Schematic\Schematic;
+use NerdsAndCompany\Schematic\Events\SourceMappingEvent;
 
 /**
  * Schematic Sources Behavior.
@@ -94,6 +95,7 @@ public function getSource(string $fieldType, string $source = null, string $inde
         /** @var Model $sourceObject */
         $sourceObject = null;
 
+        // Get service and method by source
         list($sourceType, $sourceFrom) = explode(':', $source);
         switch ($sourceType) {
             case 'editSite':
@@ -144,6 +146,18 @@ public function getSource(string $fieldType, string $source = null, string $inde
                 return $source;
         }
 
+        // Send event
+        $plugin = Craft::$app->controller->module;
+        $event = new SourceMappingEvent([
+            'source' => $source,
+            'service' => $service ?? null,
+            'method' => $method ?? null,
+        ]);
+        $plugin->trigger($plugin::EVENT_MAP_SOURCE, $event);
+        $service = $event->service;
+        $method = $event->method;
+
+        // Try service and method
         if (isset($service) && isset($method) && isset($sourceFrom)) {
             $method = $method.ucfirst($indexFrom);
             try {
diff --git a/src/Controllers/Base.php b/src/Controllers/Base.php
index 45101529..5ce0392a 100644
--- a/src/Controllers/Base.php
+++ b/src/Controllers/Base.php
@@ -53,9 +53,10 @@ protected function getDataTypes(): array
             $dataTypes = $this->applyExcludes($dataTypes);
         }
 
-        //Import fields again after all sources have been imported
+        //Import fields and usergroups again after all sources have been imported
         if (array_search('fields', $dataTypes) && count($dataTypes) > 1) {
             $dataTypes[] = 'fields';
+            $dataTypes[] = 'userGroups';
         }
 
         return $dataTypes;
diff --git a/src/Events/SourceMappingEvent.php b/src/Events/SourceMappingEvent.php
new file mode 100644
index 00000000..02c73db4
--- /dev/null
+++ b/src/Events/SourceMappingEvent.php
@@ -0,0 +1,34 @@
+<?php
+
+namespace NerdsAndCompany\Schematic\Events;
+
+use yii\base\Event;
+
+/**
+ * Schematic Source Mapping Event.
+ *
+ * Sync Craft Setups.
+ *
+ * @author    Nerds & Company
+ * @copyright Copyright (c) 2015-2018, Nerds & Company
+ * @license   MIT
+ *
+ * @see      http://www.nerds.company
+ */
+class SourceMappingEvent extends Event
+{
+    /**
+     * @var string
+     */
+    public $source;
+
+    /**
+     * @var string
+     */
+    public $service;
+
+    /**
+     * @var string
+     */
+    public $method;
+}
diff --git a/src/Schematic.php b/src/Schematic.php
index e8f707f0..2a6e867f 100644
--- a/src/Schematic.php
+++ b/src/Schematic.php
@@ -47,6 +47,7 @@
 class Schematic extends Plugin
 {
     const EVENT_RESOLVE_CONVERTER = 'resolve_converter';
+    const EVENT_MAP_SOURCE = 'map_source';
 
     /**
      * @var string