The design of the adaptive optics (AO) system for the GMT is currently being developed. The baseline system is planned around a segmented adaptive secondary mirror (ASM), with elements similar in size to current ASM's for 8 m telescopes. A facility wavefront sensing system is planned to provide AO correction at several science instrument ports. The AO system will contain a subsystem dedicated to controlling the relative phases between the seven segments of the GMT aperture. The anticipated modes include natural guide star, laser tomography, and ground layer adaptive optics. A cooled optical relay is described to provide baffling and reimaging of the focal plane to the various science ports. The laser projection system will use six beacons on an adjustable radius to support both diffraction-limited and ground layer correction modes. Modeling work, as well as science instrument design development will be integrated with this design effort to develop a concept that provides efficient diffraction-limited performance and seeing-improved capabilities for the GMT.