diff --git a/app/build.gradle b/app/build.gradle
index 401a6ea4..f5e66b50 100644
--- a/app/build.gradle
+++ b/app/build.gradle
@@ -138,6 +138,7 @@ dependencies {
     compile group: 'com.madgag.spongycastle', name: 'prov', version: '1.54.0.0'
     compile group: 'com.google.code.gson', name: 'gson', version: '1.7.2'
     compile 'com.squareup.okhttp3:logging-interceptor:3.8.0'
+    compile 'org.apache.commons:commons-collections4:4.1'
     provided 'org.projectlombok:lombok:1.16.16'
 
     // for tests
diff --git a/app/src/main/java/com/etesync/syncadapter/resource/LocalGroup.java b/app/src/main/java/com/etesync/syncadapter/resource/LocalGroup.java
index 5918ba00..5dd00b21 100644
--- a/app/src/main/java/com/etesync/syncadapter/resource/LocalGroup.java
+++ b/app/src/main/java/com/etesync/syncadapter/resource/LocalGroup.java
@@ -25,6 +25,7 @@ import com.etesync.syncadapter.App;
 
 import org.apache.commons.lang3.ArrayUtils;
 
+import java.io.ByteArrayOutputStream;
 import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.util.HashSet;
@@ -41,10 +42,13 @@ import at.bitfire.vcard4android.BatchOperation;
 import at.bitfire.vcard4android.CachedGroupMembership;
 import at.bitfire.vcard4android.Contact;
 import at.bitfire.vcard4android.ContactsStorageException;
+import ezvcard.VCardVersion;
 import lombok.Cleanup;
 import lombok.Getter;
 import lombok.ToString;
 
+import static at.bitfire.vcard4android.GroupMethod.GROUP_VCARDS;
+
 @ToString(callSuper=true)
 public class LocalGroup extends AndroidGroup implements LocalResource {
     @Getter
@@ -62,7 +66,15 @@ public class LocalGroup extends AndroidGroup implements LocalResource {
 
     @Override
     public String getContent() throws IOException, ContactsStorageException {
-        return null;
+        final Contact contact;
+        contact = getContact();
+
+        App.log.log(Level.FINE, "Preparing upload of VCard " + getUuid(), contact);
+
+        ByteArrayOutputStream os = new ByteArrayOutputStream();
+        contact.write(VCardVersion.V4_0, GROUP_VCARDS, os);
+
+        return os.toString();
     }
 
     @Override
@@ -107,7 +119,7 @@ public class LocalGroup extends AndroidGroup implements LocalResource {
     @Override
     public void prepareForUpload() throws ContactsStorageException {
         final String uid = UUID.randomUUID().toString();
-        final String newFileName = uid + ".vcf";
+        final String newFileName = uid;
 
         ContentValues values = new ContentValues(2);
         values.put(COLUMN_FILENAME, newFileName);
diff --git a/app/src/main/java/com/etesync/syncadapter/syncadapter/ContactsSyncManager.java b/app/src/main/java/com/etesync/syncadapter/syncadapter/ContactsSyncManager.java
index 98b57c34..e49c36cf 100644
--- a/app/src/main/java/com/etesync/syncadapter/syncadapter/ContactsSyncManager.java
+++ b/app/src/main/java/com/etesync/syncadapter/syncadapter/ContactsSyncManager.java
@@ -10,7 +10,9 @@ package com.etesync.syncadapter.syncadapter;
 
 import android.accounts.Account;
 import android.content.ContentProviderClient;
+import android.content.ContentProviderOperation;
 import android.content.ContentResolver;
+import android.content.ContentUris;
 import android.content.ContentValues;
 import android.content.Context;
 import android.content.SyncResult;
@@ -33,14 +35,18 @@ import com.etesync.syncadapter.resource.LocalGroup;
 import com.etesync.syncadapter.resource.LocalResource;
 
 import org.apache.commons.codec.Charsets;
+import org.apache.commons.collections4.SetUtils;
 import org.apache.commons.io.IOUtils;
 
 import java.io.ByteArrayInputStream;
+import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.io.InputStream;
+import java.util.Set;
 import java.util.logging.Level;
 
 import at.bitfire.ical4android.CalendarStorageException;
+import at.bitfire.vcard4android.BatchOperation;
 import at.bitfire.vcard4android.Contact;
 import at.bitfire.vcard4android.ContactsStorageException;
 import lombok.Cleanup;
@@ -100,6 +106,8 @@ public class ContactsSyncManager extends SyncManager {
 
         journal = new JournalEntryManager(httpClient, remote, localAddressBook.getURL());
 
+        localAddressBook.includeGroups = true;
+
         return true;
     }
 
@@ -109,12 +117,27 @@ public class ContactsSyncManager extends SyncManager {
 
         LocalAddressBook addressBook = localAddressBook();
 
-        /* groups as separate VCards: thtere are group contacts and individual contacts */
+        /* groups as separate VCards: there are group contacts and individual contacts */
 
         // mark groups with changed members as dirty
-
-        // FIXME: add back
-
+        BatchOperation batch = new BatchOperation(addressBook.provider);
+        for (LocalContact contact : addressBook.getDirtyContacts()) {
+            try {
+                App.log.fine("Looking for changed group memberships of contact " + contact.getFileName());
+                Set<Long> cachedGroups = contact.getCachedGroupMemberships(),
+                        currentGroups = contact.getGroupMemberships();
+                for (Long groupID : SetUtils.disjunction(cachedGroups, currentGroups)) {
+                    App.log.fine("Marking group as dirty: " + groupID);
+                    batch.enqueue(new BatchOperation.Operation(
+                            ContentProviderOperation.newUpdate(addressBook.syncAdapterURI(ContentUris.withAppendedId(ContactsContract.Groups.CONTENT_URI, groupID)))
+                                    .withValue(ContactsContract.Groups.DIRTY, 1)
+                                    .withYieldAllowed(true)
+                    ));
+                }
+            } catch (FileNotFoundException ignored) {
+            }
+        }
+        batch.commit();
     }
 
     @Override