ActiveSync is a mobile data synchronization app developed by Microsoft, originally released in 1996.

ActiveSync allows a mobile device to be synchronized with either a desktop PC or a server running a compatible software product.

On desktops, ActiveSync synchronizes emails, calendar, contacts and tasks with Microsoft Outlook, along with Internet bookmarks and files.

In case of Exchange Server, only emails, calendar, contacts and tasks may be synchronized.

Supported mobile devices include PDAs or smartphones running Windows Mobile, Windows CE,[1] BlackBerry 10 or iOS but not the older BlackBerry versions, Palm OS and Symbian platforms.