Risa and her group work on a range of topics in cosmology and astrophysics, with a focus on the formation of cosmological structure in the Universe, its impact on galaxy formation, and its use in determining the nature of dark matter and dark energy. Risa's group builds and analyzes numerical simulations and develops models of galaxy formation for comparison with large observational datasets, and develops new techniques to learn about the dark side of the Universe from these data.  Her group is actively involved in the ongoing Dark Energy Survey (DES), as well as the largest future planned surveys including the Dark Energy Spectroscopic Instrument (DESI) and the Large Synoptic Survey Telescope (LSST).  She is currently very interested in how small-scale structure can constrain the nature of dark matter and is the Co-PI of the SAGA survey, which is identifying dwarf galaxies around Milky Way-like galaxies.