Please note that as of October 24, 2014, the Nokia Developer Wiki will no longer be accepting user contributions, including new entries, edits and comments, as we begin transitioning to our new home, in the Windows Phone Development Wiki. We plan to move over the majority of the existing entries. Thanks for all your past and future contributions.
Detecting orientation events in Windows Phone
The article Quickstart: Screen orientation for Windows Phone explains how to specify supported orientations and react to orientation changes in Windows Phone.