diff --git a/lib/db/folder_db.dart b/lib/db/folder_db.dart
new file mode 100644
index 000000000..aa5e44a4e
--- /dev/null
+++ b/lib/db/folder_db.dart
@@ -0,0 +1,105 @@
+import 'dart:io';
+
+import 'package:path/path.dart';
+import 'package:photos/models/folder.dart';
+import 'package:sqflite/sqflite.dart';
+import 'package:path_provider/path_provider.dart';
+
+class FolderDB {
+  static final _databaseName = "ente.db";
+  static final _databaseVersion = 1;
+
+  static final table = 'folders';
+
+  static final columnId = 'id';
+  static final columnName = 'name';
+  static final columnOwner = 'owner';
+  static final columnDeviceFolder = 'device_folder';
+  static final columnSharedWith = 'shared_with';
+  static final columnUpdateTimestamp = 'update_timestamp';
+
+  FolderDB._privateConstructor();
+  static final FolderDB instance = FolderDB._privateConstructor();
+
+  static Database _database;
+  Future<Database> get database async {
+    if (_database != null) return _database;
+    _database = await _initDatabase();
+    return _database;
+  }
+
+  _initDatabase() async {
+    Directory documentsDirectory = await getApplicationDocumentsDirectory();
+    String path = join(documentsDirectory.path, _databaseName);
+    return await openDatabase(path,
+        version: _databaseVersion, onCreate: _onCreate);
+  }
+
+  Future _onCreate(Database db, int version) async {
+    await db.execute('''
+          CREATE TABLE $table (
+            $columnId INTEGER PRIMARY KEY NOT NULL,
+            $columnName TEXT NOT NULL,
+            $columnOwner TEXT NOT NULL,
+            $columnDeviceFolder TEXT NOT NULL,
+            $columnSharedWith TEXT NOT NULL,
+            $columnUpdateTimestamp INTEGER NOT NULL,
+            UNIQUE($columnOwner, $columnDeviceFolder)
+          )
+          ''');
+  }
+
+  Future<int> putFolder(Folder folder) async {
+    final db = await instance.database;
+    return await db.insert(table, _getRowForFolder(folder),
+        conflictAlgorithm: ConflictAlgorithm.replace);
+  }
+
+  Future<List<Folder>> getFolders() async {
+    final db = await instance.database;
+    final results = await db.query(
+      table,
+      orderBy: '$columnUpdateTimestamp DESC',
+    );
+    return _convertToFolders(results);
+  }
+
+  Future<int> deleteFolder(Folder folder) async {
+    final db = await instance.database;
+    return db.delete(
+      table,
+      where: '$columnId =?',
+      whereArgs: [folder.id],
+    );
+  }
+
+  List<Folder> _convertToFolders(List<Map<String, dynamic>> results) {
+    var folders = List<Folder>();
+    for (var result in results) {
+      folders.add(_getFolderFromRow(result));
+    }
+    return folders;
+  }
+
+  Map<String, dynamic> _getRowForFolder(Folder folder) {
+    var row = new Map<String, dynamic>();
+    row[columnId] = folder.id;
+    row[columnName] = folder.name;
+    row[columnOwner] = folder.owner;
+    row[columnDeviceFolder] = folder.deviceFolder;
+    row[columnSharedWith] = folder.sharedWith.toString();
+    row[columnUpdateTimestamp] = folder.updateTimestamp;
+    return row;
+  }
+
+  Folder _getFolderFromRow(Map<String, dynamic> row) {
+    return Folder(
+      row[columnId],
+      row[columnName],
+      row[columnOwner],
+      row[columnDeviceFolder],
+      Set<String>.from(row[columnSharedWith]),
+      row[columnUpdateTimestamp],
+    );
+  }
+}
diff --git a/lib/db/photo_db.dart b/lib/db/photo_db.dart
index e5ad77c46..74e490a8c 100644
--- a/lib/db/photo_db.dart
+++ b/lib/db/photo_db.dart
@@ -16,6 +16,7 @@ class PhotoDB {
   static final columnLocalId = 'local_id';
   static final columnTitle = 'title';
   static final columnDeviceFolder = 'device_folder';
+  static final columnRemoteFolderId = 'remote_folder_id';
   static final columnRemotePath = 'remote_path';
   static final columnIsDeleted = 'is_deleted';
   static final columnCreateTimestamp = 'create_timestamp';
@@ -51,6 +52,7 @@ class PhotoDB {
             $columnUploadedFileId INTEGER NOT NULL,
             $columnTitle TEXT NOT NULL,
             $columnDeviceFolder TEXT NOT NULL,
+            $columnRemoteFolderId INTEGER DEFAULT -1,
             $columnRemotePath TEXT,
             $columnIsDeleted INTEGER DEFAULT 0,
             $columnCreateTimestamp TEXT NOT NULL,
@@ -175,6 +177,15 @@ class PhotoDB {
     );
   }
 
+  Future<int> deletePhotosInRemoteFolder(int folderId) async {
+    final db = await instance.database;
+    return db.delete(
+      table,
+      where: '$columnRemoteFolderId =?',
+      whereArgs: [folderId],
+    );
+  }
+
   Future<List<String>> getDistinctPaths() async {
     final db = await instance.database;
     final rows = await db.query(
@@ -205,6 +216,22 @@ class PhotoDB {
     }
   }
 
+  Future<Photo> getLatestPhotoInRemoteFolder(int folderId) async {
+    final db = await instance.database;
+    var rows = await db.query(
+      table,
+      where: '$columnRemoteFolderId =?',
+      whereArgs: [folderId],
+      orderBy: '$columnCreateTimestamp DESC',
+      limit: 1,
+    );
+    if (rows.isNotEmpty) {
+      return _getPhotoFromRow(rows[0]);
+    } else {
+      throw ("No photo found in path");
+    }
+  }
+
   Future<Photo> getLatestPhotoAmongGeneratedIds(
       List<String> generatedIds) async {
     final db = await instance.database;
@@ -236,6 +263,7 @@ class PhotoDB {
         photo.uploadedFileId == null ? -1 : photo.uploadedFileId;
     row[columnTitle] = photo.title;
     row[columnDeviceFolder] = photo.deviceFolder;
+    row[columnRemoteFolderId] = photo.remoteFolderId;
     row[columnRemotePath] = photo.remotePath;
     row[columnCreateTimestamp] = photo.createTimestamp;
     row[columnSyncTimestamp] = photo.syncTimestamp;
@@ -249,6 +277,7 @@ class PhotoDB {
     photo.uploadedFileId = row[columnUploadedFileId];
     photo.title = row[columnTitle];
     photo.deviceFolder = row[columnDeviceFolder];
+    photo.remoteFolderId = row[columnRemoteFolderId];
     photo.remotePath = row[columnRemotePath];
     photo.createTimestamp = int.parse(row[columnCreateTimestamp]);
     photo.syncTimestamp = row[columnSyncTimestamp] == null
diff --git a/lib/folder_service.dart b/lib/folder_service.dart
index 550f8c2a7..bd8faf6fc 100644
--- a/lib/folder_service.dart
+++ b/lib/folder_service.dart
@@ -1,18 +1,77 @@
 import 'dart:developer';
 
 import 'package:dio/dio.dart';
+import 'package:logging/logging.dart';
 import 'package:photos/core/configuration.dart';
+import 'package:photos/db/folder_db.dart';
+import 'package:photos/db/photo_db.dart';
 import 'package:photos/models/folder.dart';
+import 'package:photos/models/photo.dart';
 
 class FolderSharingService {
+  final _logger = Logger("FolderSharingService");
   final _dio = Dio();
+  static final _diffLimit = 100;
 
   FolderSharingService._privateConstructor();
   static final FolderSharingService instance =
       FolderSharingService._privateConstructor();
 
   void sync() {
-    // TODO
+    getFolders().then((f) async {
+      var folders = f.toSet();
+      var currentFolders = await FolderDB.instance.getFolders();
+      for (final currentFolder in currentFolders) {
+        if (!folders.contains(currentFolder)) {
+          await FolderDB.instance.deleteFolder(currentFolder);
+          await PhotoDB.instance.deletePhotosInRemoteFolder(currentFolder.id);
+        }
+      }
+      for (final folder in folders) {
+        await syncDiff(folder);
+        await FolderDB.instance.putFolder(folder);
+      }
+    });
+  }
+
+  Future<void> syncDiff(Folder folder) async {
+    int lastSyncTimestamp = 0;
+    try {
+      Photo photo =
+          await PhotoDB.instance.getLatestPhotoInRemoteFolder(folder.id);
+      lastSyncTimestamp = photo.syncTimestamp;
+    } catch (e) {
+      // Folder has never been synced
+    }
+    var photos = await getDiff(folder.id, lastSyncTimestamp, _diffLimit);
+    await PhotoDB.instance.insertPhotos(photos);
+    if (photos.length == _diffLimit) {
+      await syncDiff(folder);
+    }
+  }
+
+  Future<List<Photo>> getDiff(
+      int folderId, int sinceTimestamp, int limit) async {
+    Response response = await _dio.get(
+      Configuration.instance.getHttpEndpoint() +
+          "/folders/diff" +
+          folderId.toString(),
+      options:
+          Options(headers: {"X-Auth-Token": Configuration.instance.getToken()}),
+      queryParameters: {
+        "sinceTimestamp": sinceTimestamp,
+        "limit": limit,
+      },
+    ).catchError((e) => _logger.severe(e));
+    if (response != null) {
+      return (response.data["diff"] as List).map((p) {
+        Photo photo = new Photo.fromJson(p);
+        photo.remoteFolderId = folderId;
+        return photo;
+      }).toList();
+    } else {
+      return null;
+    }
   }
 
   Future<List<Folder>> getFolders() async {
@@ -29,46 +88,46 @@ class FolderSharingService {
     });
   }
 
-  Future<Map<String, bool>> getSharingStatus(String path) async {
+  Future<Folder> getFolder(String deviceFolder) async {
+    return _dio
+        .get(
+          Configuration.instance.getHttpEndpoint() + "/folders/folder/",
+          queryParameters: {
+            "deviceFolder": deviceFolder,
+          },
+          options: Options(
+              headers: {"X-Auth-Token": Configuration.instance.getToken()}),
+        )
+        .then((response) => Folder.fromMap(response.data));
+  }
+
+  Future<Map<String, bool>> getSharingStatus(Folder folder) async {
     return _dio
         .get(
       Configuration.instance.getHttpEndpoint() + "/users",
       options:
           Options(headers: {"X-Auth-Token": Configuration.instance.getToken()}),
     )
-        .then((usersResponse) {
-      return getFolders().then((folders) {
-        Folder sharedFolder;
-        for (var folder in folders) {
-          if (folder.owner == Configuration.instance.getUsername() &&
-              folder.deviceFolder == path) {
-            sharedFolder = folder;
-            break;
-          }
+        .then((response) {
+      final users = (response.data["users"] as List).toList();
+      final result = Map<String, bool>();
+      for (final user in users) {
+        if (user != Configuration.instance.getUsername()) {
+          result[user] = folder.sharedWith.contains(user);
         }
-        var sharedUsers = Set<String>();
-        if (sharedFolder != null) {
-          sharedUsers.addAll(sharedFolder.sharedWith);
-        }
-        final result = Map<String, bool>();
-        (usersResponse.data["users"] as List).forEach((user) {
-          if (user != Configuration.instance.getUsername()) {
-            result[user] = sharedUsers.contains(user);
-          }
-        });
-        return result;
-      });
+      }
+      return result;
     });
   }
 
-  Future<void> shareFolder(String name, String path, Set<String> users) {
-    var folder = Folder(0, name, Configuration.instance.getUsername(), path,
-        users.toList(), -1);
+  Future<void> updateFolder(Folder folder) {
+    log("Updating folder: " + folder.toString());
     return _dio
         .put(Configuration.instance.getHttpEndpoint() + "/folders/",
             options: Options(
                 headers: {"X-Auth-Token": Configuration.instance.getToken()}),
             data: folder.toMap())
-        .then((response) => log(response.toString()));
+        .then((response) => log(response.toString()))
+        .catchError((error) => log(error.toString()));
   }
 }
diff --git a/lib/models/folder.dart b/lib/models/folder.dart
index c759f40fd..81609dc6e 100644
--- a/lib/models/folder.dart
+++ b/lib/models/folder.dart
@@ -7,7 +7,7 @@ class Folder {
   final String name;
   final String owner;
   final String deviceFolder;
-  final List<String> sharedWith;
+  final Set<String> sharedWith;
   final int updateTimestamp;
 
   Folder(
@@ -27,7 +27,7 @@ class Folder {
       map['name'],
       map['owner'],
       map['deviceFolder'],
-      List<String>.from(map['sharedWith']),
+      Set<String>.from(map['sharedWith']),
       map['updateTimestamp'],
     );
   }
@@ -43,7 +43,7 @@ class Folder {
       'name': name,
       'owner': owner,
       'deviceFolder': deviceFolder,
-      'sharedWith': sharedWith,
+      'sharedWith': sharedWith.toList(),
       'updateTimestamp': updateTimestamp,
     };
   }
@@ -61,7 +61,7 @@ class Folder {
         o.name == name &&
         o.owner == owner &&
         o.deviceFolder == deviceFolder &&
-        listEquals(o.sharedWith, sharedWith) &&
+        setEquals(o.sharedWith, sharedWith) &&
         o.updateTimestamp == updateTimestamp;
   }
 
diff --git a/lib/models/photo.dart b/lib/models/photo.dart
index 332725cb1..b9a9e44b7 100644
--- a/lib/models/photo.dart
+++ b/lib/models/photo.dart
@@ -11,6 +11,7 @@ class Photo {
   String localId;
   String title;
   String deviceFolder;
+  int remoteFolderId;
   String remotePath;
   int createTimestamp;
   int syncTimestamp;
diff --git a/lib/ui/share_folder_widget.dart b/lib/ui/share_folder_widget.dart
index 22cb31a27..0b0c965bc 100644
--- a/lib/ui/share_folder_widget.dart
+++ b/lib/ui/share_folder_widget.dart
@@ -1,6 +1,7 @@
 import 'package:flutter/material.dart';
 import 'package:flutter/widgets.dart';
 import 'package:photos/folder_service.dart';
+import 'package:photos/models/folder.dart';
 import 'package:photos/ui/loading_widget.dart';
 
 class ShareFolderWidget extends StatefulWidget {
@@ -18,15 +19,18 @@ class ShareFolderWidget extends StatefulWidget {
 }
 
 class _ShareFolderWidgetState extends State<ShareFolderWidget> {
-  Map<String, bool> _sharingStatus;
+  Folder _folder;
 
   @override
   Widget build(BuildContext context) {
     return FutureBuilder<Map<String, bool>>(
-      future: FolderSharingService.instance.getSharingStatus(widget.path),
+      future:
+          FolderSharingService.instance.getFolder(widget.path).then((folder) {
+        _folder = folder;
+        return FolderSharingService.instance.getSharingStatus(folder);
+      }),
       builder: (context, snapshot) {
         if (snapshot.hasData) {
-          _sharingStatus = snapshot.data;
           return _getSharingDialog(snapshot.data);
         } else if (snapshot.hasError) {
           return Text(snapshot.error.toString());
@@ -52,16 +56,14 @@ class _ShareFolderWidgetState extends State<ShareFolderWidget> {
           child: Text("Share"),
           onPressed: () async {
             var sharedWith = Set<String>();
-            for (var user in _sharingStatus.keys) {
-              if (_sharingStatus[user]) {
+            for (var user in sharingStatus.keys) {
+              if (sharingStatus[user]) {
                 sharedWith.add(user);
               }
             }
-            await FolderSharingService.instance.shareFolder(
-              "namewa",
-              widget.path,
-              sharedWith,
-            );
+            _folder.sharedWith.clear();
+            _folder.sharedWith.addAll(sharedWith);
+            await FolderSharingService.instance.updateFolder(_folder);
             Navigator.of(context).pop();
           },
         ),