The Advanced Camera for the Hubble Space Telescope has three cameras. The first, the Wide Field Camera, will be a high-throughput (44% at 600 nm, including the HST OTA), wide field (200 " x204 "), 4096 x 4096 pixel CCD optical and I-band camera that is half-critically sampled at 500 nm. The second, the High Resolution Camera (HRC), is a 1024 x 1024 pixel CCD camera that is critically sampled at 500 nm. The HRC has a 26 " x29 " field of view and 29% throughput at 250 nm. The HRC optical path includes a coronagraph that will improve the HST contrast near bright objects by a factor of similar to 10 at 900 nm. The third camera, the Solar-Blind Camera, is a far-ultraviolet, pulse-counting array that has a relatively high throughput (6% at 121.6 nm) over a 26 " x29 " field of view. The Advanced Camera for Surveys (ACS) will increase HST's capability for surveys and discovery by a factor of similar to 10 at 800 nm. The ACS science team will use similar to 60% of its dedicated time to make deep surveys of 15 clusters of galaxies at redshifts between 0.2 and 2. We will map the large-scale distribution of dark matter around two low redshift rich clusters and investigate the evolution of galaxies and clusters of galaxies between redshifts of 0.5 and 1. We will study young galaxies and clusters of galaxies in fields centered on high-redshift radio galaxies. HRC images of an unbiased sample of early-type galaxies will be searched for small (r similar to 100 pc) nuclear disks; subsequent spectroscopic observations of the disks will be used to measure the central masses to determine if massive black holes are present. We will use the HRC coronagraph to take broad-band, narrow-band, and polarimetric images of quasars and BL Lacs at redshifts between 0.2 and 0.5. We will use a novel polarimetric technique to measure geometric distances to galaxies and provide independent measures of H-0. The coronagraph will be used to search nearby stars for proto-planetary disks, brown dwarf companions, and planets.