diff --git a/src/app/groups/GroupAction.tsx b/src/app/groups/GroupAction.tsx
index b1f7e6d..372dded 100644
--- a/src/app/groups/GroupAction.tsx
+++ b/src/app/groups/GroupAction.tsx
@@ -23,28 +23,73 @@ async function getGroups(): Promise<Group[]> {
   );
 }
 
-export async function getGroupsFromServer(): Promise<Group[]> {
+export async function getGroupsAction(): Promise<Group[]> {
   await actionUserRequired();
 
   return await getGroups();
 }
 
-async function updateGroup(group: Group) {
+export async function updateGroupAction(group: Group, assigendUsers: string[]) {
+  await actionAdminRequired();
+
+  console.info(
+    `${group.id ? 'Updating' : 'Adding'} group ${group.name} ${group.id || ''}`
+  );
+
+  let groupId: string;
+
   if (group.id) {
     const doc = firestore.collection(GROUP_COLLECTION_ID).doc(group.id);
     await doc.set(group, { merge: true });
-    return doc.id;
+
+    groupId = group.id;
   } else {
     // new doc
     const result = await firestore.collection(GROUP_COLLECTION_ID).add(group);
-    return result.id;
+    groupId = result.id;
   }
-}
 
-export async function updateGroupFromServer(group: Group) {
-  await actionAdminRequired();
+  const userCollection = firestore.collection(USER_COLLECTION_ID);
+  const users = (await userCollection.get()).docs || [];
+  // update assigned users
+  const batch = firestore.batch();
+
+  // users to remove
+  const removeUsers = users.filter(
+    (user) =>
+      (user.data().groups || []).includes(groupId) &&
+      !assigendUsers.includes(user.id)
+  );
+  console.info(
+    `removing ${removeUsers.length} from group ${group.name}: ${removeUsers.map(
+      (u) => u.data().displayName || u.data().email
+    )}`
+  );
+  removeUsers.forEach((user) =>
+    batch.update(userCollection.doc(user.id), {
+      groups: (user.data().groups as string[]).filter((id) => id !== groupId),
+    })
+  );
+
+  // users to add
+  const addUsers = users.filter(
+    (user) =>
+      !(user.data().groups || []).includes(groupId) &&
+      assigendUsers.includes(user.id)
+  );
+  console.info(
+    `adding ${addUsers.length} to group ${group.name}: ${addUsers.map(
+      (u) => u.data().displayName || u.data().email
+    )}`
+  );
+  addUsers.forEach((user) =>
+    batch.update(userCollection.doc(user.id), {
+      groups: [...((user.data().groups as string[]) || []), groupId],
+    })
+  );
 
-  return await updateGroup(group);
+  await batch.commit();
+  return groupId;
 }
 
 async function getMyGroups(userId: string): Promise<Group[]> {
diff --git a/src/app/groups/GroupDialog.tsx b/src/app/groups/GroupDialog.tsx
index e4971f2..6b66b78 100644
--- a/src/app/groups/GroupDialog.tsx
+++ b/src/app/groups/GroupDialog.tsx
@@ -4,14 +4,22 @@ import DialogActions from '@mui/material/DialogActions';
 import DialogContent from '@mui/material/DialogContent';
 import DialogContentText from '@mui/material/DialogContentText';
 import DialogTitle from '@mui/material/DialogTitle';
-import { SelectChangeEvent } from '@mui/material/Select';
+import Select, { SelectChangeEvent } from '@mui/material/Select';
 import TextField from '@mui/material/TextField';
-import React, { useState } from 'react';
+import React, { useEffect, useMemo, useState } from 'react';
 import { Group } from './GroupAction';
+import { UserRecordExtended } from '../../common/users';
+import FormControl from '@mui/material/FormControl';
+import InputLabel from '@mui/material/InputLabel';
+import MenuItem from '@mui/material/MenuItem';
+import Checkbox from '@mui/material/Checkbox';
+import ListItemText from '@mui/material/ListItemText';
+import OutlinedInput from '@mui/material/OutlinedInput';
 
 export interface GroupDialoggOptions {
-  onClose: (item?: Group) => void;
+  onClose: (item?: Group, assigendUsers?: string[]) => void;
   group: Group;
+  users: UserRecordExtended[];
 }
 
 export const groupTextFields: { [key: string]: string } = {
@@ -19,12 +27,37 @@ export const groupTextFields: { [key: string]: string } = {
   description: 'Zusatzinfo',
 };
 
+const ITEM_HEIGHT = 48;
+const ITEM_PADDING_TOP = 8;
+const MenuProps = {
+  PaperProps: {
+    style: {
+      maxHeight: ITEM_HEIGHT * 10 + ITEM_PADDING_TOP,
+      width: 250,
+    },
+  },
+};
+
 export default function GroupDialogg({
   onClose,
   group: groupDefault,
+  users,
 }: GroupDialoggOptions) {
   const [open, setOpen] = useState(true);
   const [group, setGroup] = useState<Group>(groupDefault);
+  const [assigendUsers, setAssigendUsers] = useState<string[]>([]);
+
+  const userMap = Object.fromEntries(users.map((user) => [user.uid, user]));
+
+  useEffect(() => {
+    setAssigendUsers(
+      users
+        .filter(
+          (user) => group.id && user.groups && user.groups.includes(group.id)
+        )
+        .map((user) => user.uid)
+    );
+  }, [group.id, users]);
 
   const onChange =
     (field: string) =>
@@ -59,6 +92,46 @@ export default function GroupDialogg({
             value={((group as any)[key] as string) || ''}
           />
         ))}
+
+        <FormControl fullWidth variant="standard">
+          <InputLabel id={`firecall-item-users-label`}>
+            Benutzer der Gruppe
+          </InputLabel>
+          <Select
+            labelId={`firecall-item-users-label`}
+            id={`firecall-item-users`}
+            multiple={true}
+            value={assigendUsers}
+            label="Assigned Users"
+            input={<OutlinedInput label="Assigned Users" />}
+            MenuProps={MenuProps}
+            renderValue={(selected) =>
+              selected
+                .map((key) => userMap[key])
+                .filter((v) => v)
+                .map((user) => `${user.displayName || user.email}`)
+                .join(', ')
+            }
+            onChange={(event) => {
+              const {
+                target: { value },
+              } = event;
+              // On autofill we get a stringified value.
+              setAssigendUsers(
+                typeof value === 'string' ? value.split(',') : value
+              );
+            }}
+          >
+            {users.map((user) => (
+              <MenuItem key={`user-for-group-${user.uid}`} value={user.uid}>
+                <Checkbox checked={assigendUsers.indexOf(user.uid) > -1} />
+                <ListItemText
+                  primary={`${user.displayName || ''} (${user.email})`}
+                />
+              </MenuItem>
+            ))}
+          </Select>
+        </FormControl>
       </DialogContent>
       <DialogActions>
         <Button
@@ -72,7 +145,7 @@ export default function GroupDialogg({
         <Button
           onClick={() => {
             setOpen(false);
-            onClose(group);
+            onClose(group, assigendUsers);
           }}
         >
           Aktualisieren
diff --git a/src/app/groups/page.tsx b/src/app/groups/page.tsx
index 0734e65..1c3b464 100644
--- a/src/app/groups/page.tsx
+++ b/src/app/groups/page.tsx
@@ -3,6 +3,7 @@
 import AddIcon from '@mui/icons-material/Add';
 import DeleteIcon from '@mui/icons-material/Delete';
 import EditIcon from '@mui/icons-material/Edit';
+import RefreshIcon from '@mui/icons-material/Refresh';
 import Box from '@mui/material/Box';
 import Fab from '@mui/material/Fab';
 import Grid from '@mui/material/Grid';
@@ -10,12 +11,14 @@ import IconButton from '@mui/material/IconButton';
 import Tooltip from '@mui/material/Tooltip';
 import Typography from '@mui/material/Typography';
 import React, { useCallback, useEffect, useState } from 'react';
+import { UserRecordExtended } from '../../common/users';
 import ConfirmDialog from '../../components/dialogs/ConfirmDialog';
+import { getUsers } from '../users/action';
 import {
   deleteGroupAction,
-  getGroupsFromServer,
+  getGroupsAction,
   Group,
-  updateGroupFromServer,
+  updateGroupAction,
 } from './GroupAction';
 import GroupDialog from './GroupDialog';
 
@@ -53,11 +56,18 @@ function GroupRowButtons({ row, editFn, deleteFn }: UserRowButtonParams) {
   );
 }
 
-function useGroupList(): [Group[], () => Promise<Group[]>] {
+function useGroupList(): [
+  Group[],
+  () => Promise<Group[]>,
+  UserRecordExtended[]
+] {
   const [groups, setGroups] = useState<Group[]>([]);
+  const [users, setUsers] = useState<UserRecordExtended[]>([]);
   const getGroups = useCallback(async () => {
-    const newGroups = await getGroupsFromServer();
+    const newGroups = await getGroupsAction();
+    const users = await getUsers();
     setGroups(newGroups);
+    setUsers(users);
     return newGroups;
   }, []);
 
@@ -65,14 +75,14 @@ function useGroupList(): [Group[], () => Promise<Group[]>] {
     getGroups();
   }, [getGroups]);
 
-  return [groups, getGroups];
+  return [groups, getGroups, users];
 }
 
-export default function Users() {
+export default function Groups() {
   const [showEditDialog, setShowEditDialog] = useState(false);
   const [isConfirmOpen, setIsConfirmOpen] = useState(false);
   const [editGroup, setEditGroup] = useState<Group>();
-  const [groups, getGroups] = useGroupList();
+  const [groups, getGroups, users] = useGroupList();
 
   const editAction = useCallback(async (group: Group) => {
     setEditGroup(group);
@@ -101,6 +111,9 @@ export default function Users() {
       <Box sx={{ p: 2, height: '70vh' }}>
         <Typography variant="h3" gutterBottom>
           Groups
+          <IconButton onClick={() => getGroups()}>
+            <RefreshIcon />
+          </IconButton>
         </Typography>
         <Grid container>
           <Grid item xs={2} md={2} lg={2}></Grid>
@@ -149,12 +162,13 @@ export default function Users() {
       {showEditDialog && editGroup && (
         <GroupDialog
           group={editGroup}
-          onClose={async (group) => {
+          users={users}
+          onClose={async (group, assigendUsers) => {
             setShowEditDialog(false);
-            if (group) {
-              await updateGroupFromServer(group);
-              await getGroups();
+            if (group && assigendUsers) {
+              await updateGroupAction(group, assigendUsers);
             }
+            await getGroups();
           }}
         />
       )}
diff --git a/src/app/users/page.tsx b/src/app/users/page.tsx
index 165a88b..f7ab82b 100644
--- a/src/app/users/page.tsx
+++ b/src/app/users/page.tsx
@@ -3,23 +3,22 @@
 import BlockIcon from '@mui/icons-material/Block';
 import CheckIcon from '@mui/icons-material/Check';
 import EditIcon from '@mui/icons-material/Edit';
+import RefreshIcon from '@mui/icons-material/Refresh';
 import Box from '@mui/material/Box';
+import Grid from '@mui/material/Grid';
 import IconButton from '@mui/material/IconButton';
 import Tooltip from '@mui/material/Tooltip';
 import Typography from '@mui/material/Typography';
 import { green, red } from '@mui/material/colors';
-import { DataGrid, GridColDef } from '@mui/x-data-grid';
-import { useCallback, useEffect, useMemo, useState } from 'react';
+import { GridColDef } from '@mui/x-data-grid';
+import React, { useCallback, useEffect, useMemo, useState } from 'react';
 import { feuerwehren } from '../../common/feuerwehren';
 import { UserRecordExtended } from '../../common/users';
 import UserRecordExtendedDialog from '../../components/users/UserDialog';
+import useFirebaseCollection from '../../hooks/useFirebaseCollection';
 import useUpdateUser from '../../hooks/useUpdateUser';
 import useUserList from '../../hooks/useUserList';
-import useFirebaseCollection from '../../hooks/useFirebaseCollection';
 import { Group } from '../groups/GroupAction';
-import Grid from '@mui/material/Grid';
-import React from 'react';
-import { Refresh } from '@mui/icons-material';
 
 interface UserRowButtonParams {
   row: UserRecordExtended;
@@ -155,7 +154,7 @@ export default function Users() {
         <Typography variant="h3" gutterBottom>
           Users{' '}
           <IconButton onClick={() => fetchUsers()}>
-            <Refresh />
+            <RefreshIcon />
           </IconButton>
         </Typography>
         <Grid container>
diff --git a/src/components/users/UserDialog.tsx b/src/components/users/UserDialog.tsx
index cbdad19..f9c56a2 100644
--- a/src/components/users/UserDialog.tsx
+++ b/src/components/users/UserDialog.tsx
@@ -1,4 +1,5 @@
 import Button from '@mui/material/Button';
+import Checkbox from '@mui/material/Checkbox';
 import Dialog from '@mui/material/Dialog';
 import DialogActions from '@mui/material/DialogActions';
 import DialogContent from '@mui/material/DialogContent';
@@ -8,26 +9,22 @@ import FormControl from '@mui/material/FormControl';
 import FormControlLabel from '@mui/material/FormControlLabel';
 import FormGroup from '@mui/material/FormGroup';
 import InputLabel from '@mui/material/InputLabel';
+import ListItemText from '@mui/material/ListItemText';
 import MenuItem from '@mui/material/MenuItem';
+import OutlinedInput from '@mui/material/OutlinedInput';
 import Select, { SelectChangeEvent } from '@mui/material/Select';
 import Switch from '@mui/material/Switch';
 import TextField from '@mui/material/TextField';
-import React, { useMemo, useState } from 'react';
+import React, { useState } from 'react';
 import { feuerwehren } from '../../common/feuerwehren';
 import { UserRecordExtended, userTextFields } from '../../common/users';
-import OutlinedInput from '@mui/material/OutlinedInput';
-import Checkbox from '@mui/material/Checkbox';
-import ListItemText from '@mui/material/ListItemText';
-import { useFirecallId } from '../../hooks/useFirecall';
-import useFirebaseCollection from '../../hooks/useFirebaseCollection';
-import { Group } from '../../app/groups/GroupAction';
 
 const ITEM_HEIGHT = 48;
 const ITEM_PADDING_TOP = 8;
 const MenuProps = {
   PaperProps: {
     style: {
-      maxHeight: ITEM_HEIGHT * 4.5 + ITEM_PADDING_TOP,
+      maxHeight: ITEM_HEIGHT * 10 + ITEM_PADDING_TOP,
       width: 250,
     },
   },