The circumgalactic medium (CGM) not only holds the majority of a galactic halo’s baryons, but it is an essential piece of the puzzle for the understanding of how galaxies form and evolve. I will divide my talk into three portions, and use hydrodynamic simulations to help address central questions in how today’s galaxies got that way. The first portion involves the surprising calculation that galaxies place the majority of the heavy elements they nucleosynthesize into the CGM via superwind feedback. I will argue that even as enriched gas recycles back onto galaxies, a Milky Way-like galaxy will still have most of its metals yielded from supernovae in the CGM. Then I will discuss a central debate emerging within our field— is there a causal or coincidental relationship between galactic star formation plus AGN activity and the amount of metals observed CGM? The currently unknown answer involves observing and understanding the nature of galaxy-black hole-CGM co-evolution. Finally, I will touch upon reasons we need more observations of the CGM, and how understanding the dynamics of baryonic haloes can reveal clues for what determines galaxy morphologies.