The Future US Cosmology Program

There is now a standard cosmological theory that is consistent with all extant data, including for the first time cosmological measurements of very high accuracy. The ``concordance model,'' however, contains three elements with weak theoretical motivation and no laboratory verification: a dark matter particle, a non-zero cosmological constant, and a field to drive inflation. Where do we go from here? I will describe observational opportunities that exist in several areas: (1) Testing General Relativity on large scales, where it underlies the concordance model; (2) Detecting signals that originate during cosmological epochs that are presently unobserved: gravity waves from the early Universe, and 21-cm signals from redshifts 6--50; (3) High-precision measures of the expansion and matter-clustering history of the Universe, to gain further information on the ``dark'' phenomena; (4) More detailed understanding of the paradigm that galaxies form by collapse of baryons into dark-matter potential wells. I will describe US facilities proposed to exploit these observational opportunities.