  The technique of intensity mapping (IM) has emerged as a powerful tool to
explore the universe at $z < 6$. IM measures the integrated emission from
sources over a broad range of frequencies, unlocking significantly more
information than traditional galaxy surveys. Astrophysical uncertainties,
however, constitute an important systematic in our attempts to constrain
cosmology with IM. I describe an innovative approach which allows us to fully
utilize our current knowledge of astrophysics in order to develop cosmological
forecasts from IM. This framework can be used to exploit synergies with other
complementary surveys, thereby opening up the fascinating possibility of
constraining physics beyond $\Lambda$CDM from future IM observations.
