Tremendous progress has been made over the last decade in our empirical and theoretical understanding of how galaxies form and evolve across cosmic time. In particular, state-of-the-art cosmological simulations can not only match the large-scale statistical properties of galaxies, but they can also successfully reproduce the observed small-scale features. However, it appears that these models have fallen short in matching the empirical properties of diffuse gas in the circumgalactic space, which constitutes 90% of all baryons in the universe. The circumgalactic medium contains the fuel for future star formation and the record of past feedback, making it uniquely sensitive to the physics of baryonic flows. I will summarize recent progress in characterizing this gas reservoir and introduce new surveys designed to address some of the remaining questions/puzzles.
