GEMs is a large-area (800 arcmin 2) two-color (F606W and F850LP) imaging survey with the Advanced Camera for Surveys on the Hubble Space Telescope. Centered on the Chandra Deep Field-South, it covers an area of ~ 28'x28', or about 120 HDF areas, to a depth of MAB(F606W)=28.5(5s) for compact sources. Focusing on the redshift range ~ 0.2<z<1.1, GEMS provides morphologies and structural parameters for nearly 10,000 galaxies where redshift estimates, luminosities, and SEDs exist from COMBO-17.