Systems and methods for requesting and providing assistance data for a satellite positioning system are described herein. A method as described herein includes receiving, at a base station over a wireless communication link, a first message from a mobile station, wherein the first message comprises a first field identifying requested assistance data associated with a first Satellite Positioning System (SPS) and a second field identifying a requested format of the requested assistance data, and wherein the requested assistance data are available in a plurality of formats that includes the requested format; and transmitting a second message from the base station to the mobile station over the wireless communication link, wherein the second message includes the requested assistance data in the requested format.