  The Joint Dark Energy Mission (JDEM) is expected to have a field-of-view that
is several orders of magnitude larger than that of current instruments on the
Hubble Space Telescope, with only slightly reduced sensitivity and resolution.
This contribution gives a brief discussion of the impact that JDEM would have
on studies of galaxies in clusters at 0.5<z<2 and of the most massive galaxies
at higher redshift. Of particular importance is JDEMs unique wide-field near-IR
capability, enabling the selection and morphological study of high redshift
galaxies in the rest-frame optical rather than the rest-frame ultra-violet.
