diff --git a/lib/plankton/plankton.d.ts b/lib/plankton/plankton.d.ts
index 30c6b9f..9da3c53 100644
--- a/lib/plankton/plankton.d.ts
+++ b/lib/plankton/plankton.d.ts
@@ -882,6 +882,9 @@ declare namespace lib_plankton.call {
     /**
      */
     export function sleep(seconds: float): Promise<void>;
+    /**
+     */
+    export function null_prop<type_value_from, type_value_to>(value_from: (null | type_value_from), function_: ((value: type_value_from) => type_value_to)): (null | type_value_to);
     export {};
 }
 declare namespace lib_plankton.file {
diff --git a/lib/plankton/plankton.js b/lib/plankton/plankton.js
index 8509b96..6a8b172 100644
--- a/lib/plankton/plankton.js
+++ b/lib/plankton/plankton.js
@@ -2043,6 +2043,16 @@ var lib_plankton;
             }));
         }
         call.sleep = sleep;
+        /**
+         */
+        function null_prop(value_from, function_) {
+            return ((value_from === null)
+                ?
+                    null
+                :
+                    function_(value_from));
+        }
+        call.null_prop = null_prop;
     })(call = lib_plankton.call || (lib_plankton.call = {}));
 })(lib_plankton || (lib_plankton = {}));
 /*
@@ -3792,10 +3802,10 @@ var lib_plankton;
             options = Object.assign({
                 "compare_value": instance_compare
             }, options);
-            if (is_empty(list)) {
+            /*if (is_empty<type_element>(list)) {
                 throw (new Error("the max-arg of an empty list is not defined"));
             }
-            else {
+            else */ {
                 return (list
                     .reduce(function (result, element, index) {
                     var value = target_function(element);
diff --git a/source/data/localization/deu.loc.json b/source/data/localization/deu.loc.json
index cf92d58..f5ec083 100644
--- a/source/data/localization/deu.loc.json
+++ b/source/data/localization/deu.loc.json
@@ -47,7 +47,8 @@
 		"calendar.access.access": "Zugriff",
 		"calendar.access.public": "öffentlich",
 		"calendar.access.default_level": "Standard",
-		"calendar.access.attributed": "Zuweisungen",
+		"calendar.access.attributed_group": "Gruppen-Zuweisungen",
+		"calendar.access.attributed_user": "Nutzer-Zuweisungen",
 		"widget.listview.add": "Termin anlegen",
 		"widget.weekview.controls.year": "Jahr",
 		"widget.weekview.controls.week": "Woche",
diff --git a/source/data/localization/eng.loc.json b/source/data/localization/eng.loc.json
index beec643..47785ec 100644
--- a/source/data/localization/eng.loc.json
+++ b/source/data/localization/eng.loc.json
@@ -47,7 +47,8 @@
 		"calendar.access.access": "access",
 		"calendar.access.public": "public",
 		"calendar.access.default_level": "default",
-		"calendar.access.attributed": "attributed",
+		"calendar.access.attributed_group": "group attributed",
+		"calendar.access.attributed_user": "user attributed",
 		"widget.listview.add": "add event",
 		"widget.weekview.controls.year": "year",
 		"widget.weekview.controls.week": "week",
diff --git a/source/helpers.ts b/source/helpers.ts
index 92a791a..34b0292 100644
--- a/source/helpers.ts
+++ b/source/helpers.ts
@@ -151,7 +151,42 @@ namespace _dali.helpers
 	
 	/**
 	 */
-	export function input_attributed_access(
+	export function input_attributed_access_group(
+		groups : Array<{id : _dali.type_group_id; object : _dali.type_group_object;}>
+	)
+	: lib_plankton.zoo_input.class_input_hashmap<
+		_dali.type_group_id,
+		_dali.enum_access_level
+	>
+	{
+		return (
+			new lib_plankton.zoo_input.class_input_hashmap<_dali.type_group_id, _dali.enum_access_level>(
+				// hash_key
+				(group_id) => group_id.toFixed(0),
+				// key_input_factory
+				() => new lib_plankton.zoo_input.class_input_wrapped<string, int>(
+					new lib_plankton.zoo_input.class_input_selection(
+						groups
+						.map(
+							(group) => ({
+								"value": group.id.toFixed(0),
+								"label": group.object.label,
+							})
+						)
+					),
+					x => parseInt(x),
+					x => x.toFixed(0)
+				),
+				// value_input_factory
+				() => input_access_level()
+			)
+		);
+	}
+	
+	
+	/**
+	 */
+	export function input_attributed_access_user(
 		users : Array<{id : _dali.type_user_id; name : string;}>
 	)
 	: lib_plankton.zoo_input.class_input_hashmap<
diff --git a/source/model.ts b/source/model.ts
index fe14509..b42bcf4 100644
--- a/source/model.ts
+++ b/source/model.ts
@@ -4,6 +4,12 @@ namespace _dali.model
 	/**
 	 */
 	type type_state = {
+		groups : Array<
+			{
+				id : _dali.type_group_id;
+				object : _dali.type_group_object;
+			}
+		>;
 		users : Array<
 			{
 				id : _dali.type_user_id;
@@ -110,6 +116,23 @@ namespace _dali.model
 	}
 	
 	
+	/**
+	 */
+	export async function group_list(
+	)
+	: Promise<
+		Array<
+			{
+				id : _dali.type_group_id;
+				object : _dali.type_group_object;
+			}
+		>
+	>
+	{
+		return Promise.resolve(_state.groups);
+	}
+	
+	
 	/**
 	 */
 	export async function user_list(
@@ -196,12 +219,30 @@ namespace _dali.model
 				"access": {
 					"public": data.access.public,
 					"default_level": _dali.access_level_decode(data.access.default_level),
-					"attributed": lib_plankton.map.hashmap.implementation_map(
+					"attributed_group": lib_plankton.map.hashmap.implementation_map(
 						lib_plankton.map.hashmap.make(
 							x => x.toFixed(0),
 							{
 								"pairs": (
-									data.access.attributed
+									data.access.attributed_group
+									.map(
+										(entry) => (
+											{
+												"key": entry.group_id,
+												"value": _dali.access_level_decode(entry.level),
+											}
+										)
+									)
+								),
+							}
+						)
+					),
+					"attributed_user": lib_plankton.map.hashmap.implementation_map(
+						lib_plankton.map.hashmap.make(
+							x => x.toFixed(0),
+							{
+								"pairs": (
+									data.access.attributed_user
 									.map(
 										(entry) => (
 											{
@@ -244,8 +285,19 @@ namespace _dali.model
 				"access": {
 					"public": calendar_object.access.public,
 					"default_level": _dali.access_level_encode(calendar_object.access.default_level),
-					"attributed": (
-						lib_plankton.map.dump(calendar_object.access.attributed)
+					"attributed_group": (
+						lib_plankton.map.dump(calendar_object.access.attributed_group)
+						.map(
+							(pair) => (
+								{
+									"group_id": pair.key,
+									"level": _dali.access_level_encode(pair.value),
+								}
+							)
+						)
+					),
+					"attributed_user": (
+						lib_plankton.map.dump(calendar_object.access.attributed_user)
 						.map(
 							(pair) => (
 								{
@@ -254,7 +306,7 @@ namespace _dali.model
 								}
 							)
 						)
-					)
+					),
 				},
 				/**
 				 * @todo
@@ -298,15 +350,24 @@ namespace _dali.model
 				"access": {
 					"public": calendar_object.access.public,
 					"default_level": _dali.access_level_encode(calendar_object.access.default_level),
-					"attributed": (
-						lib_plankton.map.dump(calendar_object.access.attributed)
+					"attributed_group": (
+						lib_plankton.map.dump(calendar_object.access.attributed_group)
+						.map(
+							(pair) => ({
+								"group_id": pair.key,
+								"level": _dali.access_level_encode(pair.value),
+							})
+						)
+					),
+					"attributed_user": (
+						lib_plankton.map.dump(calendar_object.access.attributed_user)
 						.map(
 							(pair) => ({
 								"user_id": pair.key,
 								"level": _dali.access_level_encode(pair.value),
 							})
 						)
-					)
+					),
 				},
 			}
 		);
@@ -554,13 +615,8 @@ namespace _dali.model
 	: Promise<void>
 	{
 		_state = {
-			"users": (
-				_dali.is_logged_in()
-				?
-				(await _dali.backend.user_list())
-				:
-				[]
-			),
+			"groups": [],
+			"users": [],
 			"calendars": lib_plankton.map.hashmap.implementation_map(
 				lib_plankton.map.hashmap.make(
 					calendar_id => calendar_id.toFixed(0)
@@ -577,6 +633,20 @@ namespace _dali.model
 		
 		_dali.listen_login(
 			async () => {
+				_state.groups = (
+					(await _dali.backend.group_list())
+					.map(
+						entry => (
+							{
+								"id": entry.id,
+								"object": {
+									"name": entry.name,
+									"label": entry.label,
+								}
+							}
+						)
+					)
+				);
 				_state.users = await _dali.backend.user_list();
 				await sync_calendars();
 				lib_plankton.map.clear(_state.events);
@@ -586,6 +656,7 @@ namespace _dali.model
 		);
 		_dali.listen_logout(
 			async () => {
+				_state.groups = [];
 				_state.users = [];
 				await sync_calendars();
 				lib_plankton.map.clear(_state.events);
diff --git a/source/pages/overview/logic.ts b/source/pages/overview/logic.ts
index 374caab..bb026aa 100644
--- a/source/pages/overview/logic.ts
+++ b/source/pages/overview/logic.ts
@@ -136,6 +136,7 @@ namespace _dali.pages.overview
 			: Promise<void>
 			{
 				const widget = new _dali.widgets.calendar_edit.class_widget_calendar_edit(
+					await _dali.model.group_list(),
 					await _dali.model.user_list(),
 					{
 						"name": "",
@@ -143,7 +144,18 @@ namespace _dali.pages.overview
 						"access": {
 							"public": false,
 							"default_level": _dali.enum_access_level.view,
-							"attributed": lib_plankton.map.hashmap.implementation_map<
+							"attributed_group": lib_plankton.map.hashmap.implementation_map<
+								_dali.type_group_id,
+								_dali.enum_access_level
+							>(
+								lib_plankton.map.hashmap.make<
+									_dali.type_group_id,
+									_dali.enum_access_level
+								>(
+									group_id => group_id.toFixed(0),
+								)
+							),
+							"attributed_user": lib_plankton.map.hashmap.implementation_map<
 								_dali.type_user_id,
 								_dali.enum_access_level
 							>(
@@ -235,6 +247,7 @@ namespace _dali.pages.overview
 						calendar_id
 					);
 					const widget = new _dali.widgets.calendar_edit.class_widget_calendar_edit(
+						await _dali.model.group_list(),
 						await _dali.model.user_list(),
 						calendar_object,
 						{
@@ -290,75 +303,82 @@ namespace _dali.pages.overview
 			)
 			: Promise<void>
 			{
-				const widget = new _dali.widgets.event_edit.class_widget_event_edit(
-					(await get_available_calendars()),
-					{
-						"calendar_id": null,
-						"event_name": "",
-						"event_begin": lib_plankton.call.convey(
-							date,
-							[
-								x => ({
-									"timezone_shift": 0,
-									"date": date,
-									"time": {"hour": 12, "minute": 0, "second": 0}
-								}),
-								lib_plankton.pit.from_datetime,
-								x => lib_plankton.pit.shift_hour(x, 0),
-								lib_plankton.pit.to_datetime,
-							]
-						),
-						"event_end": lib_plankton.call.convey(
-							date,
-							[
-								x => ({
-									"timezone_shift": 0,
-									"date": date,
-									"time": {"hour": 12, "minute": 0, "second": 0}
-								}),
-								lib_plankton.pit.from_datetime,
-								x => lib_plankton.pit.shift_hour(x, +1),
-								lib_plankton.pit.to_datetime,
-							]
-						),
-						"event_location": null,
-						"event_link": null,
-						"event_description": null,
-					},
-					{
-						"read_only": false,
-						"action_cancel": () => {
-							_dali.overlay.toggle({"mode": false});
+				if (! _dali.is_logged_in())
+				{
+					// do nothing
+				}
+				else
+				{
+					const widget = new _dali.widgets.event_edit.class_widget_event_edit(
+						(await get_available_calendars()),
+						{
+							"calendar_id": null,
+							"event_name": "",
+							"event_begin": lib_plankton.call.convey(
+								date,
+								[
+									x => ({
+										"timezone_shift": 0,
+										"date": date,
+										"time": {"hour": 12, "minute": 0, "second": 0}
+									}),
+									lib_plankton.pit.from_datetime,
+									x => lib_plankton.pit.shift_hour(x, 0),
+									lib_plankton.pit.to_datetime,
+								]
+							),
+							"event_end": lib_plankton.call.convey(
+								date,
+								[
+									x => ({
+										"timezone_shift": 0,
+										"date": date,
+										"time": {"hour": 12, "minute": 0, "second": 0}
+									}),
+									lib_plankton.pit.from_datetime,
+									x => lib_plankton.pit.shift_hour(x, +1),
+									lib_plankton.pit.to_datetime,
+								]
+							),
+							"event_location": null,
+							"event_link": null,
+							"event_description": null,
 						},
-						"action_add": (data) => {
-							_dali.model.event_add(
-								data.calendar_id,
-								{
-									"name": data.event_name,
-									"begin": data.event_begin,
-									"end": data.event_end,
-									"location": data.event_location,
-									"link": data.event_link,
-									"description": data.event_description,
-								}
-							)
-							.then(
-								() => {
-									update_entries();
-									_dali.overlay.toggle({"mode": false});
-								}
-							)
-							.catch(
-								(reason) => {
-									// todo
-								}
-							);
-						},
-					}
-				);
-				_dali.overlay.clear();
-				_dali.overlay.toggle({"mode": true});
-				await widget.load(_dali.overlay.get_content_element());
+						{
+							"read_only": false,
+							"action_cancel": () => {
+								_dali.overlay.toggle({"mode": false});
+							},
+							"action_add": (data) => {
+								_dali.model.event_add(
+									data.calendar_id,
+									{
+										"name": data.event_name,
+										"begin": data.event_begin,
+										"end": data.event_end,
+										"location": data.event_location,
+										"link": data.event_link,
+										"description": data.event_description,
+									}
+								)
+								.then(
+									() => {
+										update_entries();
+										_dali.overlay.toggle({"mode": false});
+									}
+								)
+								.catch(
+									(reason) => {
+										// todo
+									}
+								);
+							},
+						}
+					);
+					_dali.overlay.clear();
+					_dali.overlay.toggle({"mode": true});
+					await widget.load(_dali.overlay.get_content_element());
+				}
 			}
 			
 			/**
diff --git a/source/resources/backend.ts b/source/resources/backend.ts
index 3fc73d1..fc43fb7 100644
--- a/source/resources/backend.ts
+++ b/source/resources/backend.ts
@@ -411,6 +411,28 @@ namespace _dali.backend
 	}
 	
 	
+	/**
+	 */
+	export function group_list(
+	)
+	: Promise<
+		Array<
+			{
+				id : int;
+				name : string;
+				label : string;
+			}
+		>
+	>
+	{
+		return call(
+			lib_plankton.http.enum_method.get,
+			"/groups",
+			null
+		);
+	}
+	
+	
 	/**
 	 */
 	export function user_list(
@@ -512,12 +534,18 @@ namespace _dali.backend
 			access : {
 				public : boolean;
 				default_level : string;
-				attributed : Array<
+				attributed_group : Array<
+					{
+						group_id : int;
+						level : string;
+					}
+				>;
+				attributed_user : Array<
 					{
 						user_id : int;
 						level : string;
 					}
-				>
+				>;
 			};
 			resource_id : int;
 		}			
@@ -544,7 +572,13 @@ namespace _dali.backend
 			access : {
 				public : boolean;
 				default_level : string;
-				attributed : Array<
+				attributed_group : Array<
+					{
+						group_id : int;
+						level : string;
+					}
+				>;
+				attributed_user : Array<
 					{
 						user_id : int;
 						level : string;
@@ -595,7 +629,13 @@ namespace _dali.backend
 			access : {
 				public : boolean;
 				default_level : string;
-				attributed : Array<
+				attributed_group : Array<
+					{
+						group_id : int;
+						level : string;
+					}
+				>;
+				attributed_user : Array<
 					{
 						user_id : int;
 						level : string;
diff --git a/source/types.ts b/source/types.ts
index 1f7b695..7c79492 100644
--- a/source/types.ts
+++ b/source/types.ts
@@ -14,6 +14,19 @@ namespace _dali
 	}
 	
 	
+	/**
+	 */
+	export type type_group_id = int;
+	
+	
+	/**
+	 */
+	export type type_group_object = {
+		name : string;
+		label : string;
+	};
+	
+	
 	/**
 	 */
 	export type type_user_id = int;
@@ -23,6 +36,7 @@ namespace _dali
 	 */
 	export type type_user_object = {
 		name : string;
+		label : string;
 		email_address : (
 			null
 			|
@@ -137,7 +151,11 @@ namespace _dali
 		access : {
 			public : boolean;
 			default_level : enum_access_level;
-			attributed : lib_plankton.map.type_map<
+			attributed_group : lib_plankton.map.type_map<
+				type_group_id,
+				enum_access_level
+			>;
+			attributed_user : lib_plankton.map.type_map<
 				type_user_id,
 				enum_access_level
 			>;
diff --git a/source/widgets/calendar_edit/logic.ts b/source/widgets/calendar_edit/logic.ts
index a5b54e4..9b3e970 100644
--- a/source/widgets/calendar_edit/logic.ts
+++ b/source/widgets/calendar_edit/logic.ts
@@ -7,6 +7,11 @@ namespace _dali.widgets.calendar_edit
 		implements lib_plankton.zoo_widget.interface_widget
 	{
 		
+		/**
+		 */
+		private groups : Array<{id : _dali.type_group_id; object : _dali.type_group_object;}>;
+		
+		
 		/**
 		 */
 		private users : Array<{id : _dali.type_user_id; name : string;}>;
@@ -45,6 +50,7 @@ namespace _dali.widgets.calendar_edit
 		/**
 		 */
 		public constructor(
+			groups : Array<{id : _dali.type_group_id; object : _dali.type_group_object;}>,
 			users : Array<{id : _dali.type_user_id; name : string;}>,
 			initial_value : _dali.type_calendar_object,
 			{
@@ -67,6 +73,7 @@ namespace _dali.widgets.calendar_edit
 			}
 		)
 		{
+			this.groups = groups;
 			this.users = users;
 			this.initial_value = initial_value;
 			this.read_only = read_only;
@@ -121,9 +128,14 @@ namespace _dali.widgets.calendar_edit
 										"label": lib_plankton.translate.get("calendar.access.default_level"),
 									},
 									{
-										"name": "attributed",
-										"input": _dali.helpers.input_attributed_access(this.users),
-										"label": lib_plankton.translate.get("calendar.access.attributed"),
+										"name": "attributed_group",
+										"input": _dali.helpers.input_attributed_access_group(this.groups),
+										"label": lib_plankton.translate.get("calendar.access.attributed_group"),
+									},
+									{
+										"name": "attributed_user",
+										"input": _dali.helpers.input_attributed_access_user(this.users),
+										"label": lib_plankton.translate.get("calendar.access.attributed_user"),
 									},
 								]
 							),