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 played a leading role in the Dark Energy Survey, and is now actively working on data from the Dark Energy Spectroscopic Instrument (DESI), as well as preparing for data from Rubin Observatory's Legacy Survey of Space and Time (LSST) and the Roman Space Telescope.  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 100 Milky Way-like systems.