An extensible device synchronization architecture and user interface is provided. A variety of device classes are supported, and support is also provided for mass storage, WMDM, MTP, AS, etc. An extensible UI model is provided that allows content type specific setting UI to plug-in. Support for 2-way synchronization is also provided. The synchronization architecture includes a content type user experience level, and a synchronization engine layer, with handlers and a synchronization engine API which handlers can use to manage their item level synchronization relationships and implement the semantics of the synchronization. In addition, the content that is being synchronized may be transformed so that the user's experience on the destination device (e.g., mobile phone, portable audio player, PDA, other type of personal or handheld computer, etc.) is optimized and these transforms are also extensible.