Bodenheimer, Peter AST 96-18548 The discovery of extrasolar planets around solar-type stars, and the observational evidence that many very young stars are surrounded by proto-stellar disks, indicate that disk and planet formation occur frequently. The characteristics of planetary systems and the early evolution of young stellar objects are determined by the formation, evolution, and the dispersal of the disks that surround forming stars. Drs. Bodenheimer and Lin will investigate the basic physical processes that determine fundamental aspects of disk evolution : 1) the formation of protostellar disks, 2) the disk evolution which sets the stage for protoplanetary formation, and 3) the depletion of the residual disks. Their calculations will help in identifying the disk evolutionary timescales and the likely outcome of protoplanet formation.