COSMOS (P.I. Nicholas Scoville, California Institute of Technology, USA/CA) is an HST Treasury Program to survey a 2 square degree equatorial field, centered on RA=10:00:28.6 and DEC=+02:12:21.0 with the ACS in the I band of the VIMOS equatorial field. Parallel observations with WFPC2 and NICMOS were also obtained.