Empirically demonstrating the association of metal-line absorber lines with galaxies has a long, rich history from the earliest theoretical predictions in the mid 1960s to observational confirmation in the 1990s. From that point onward, quasar absorption line studies became a powerful tool for characterizing the gaseous halos of galaxies. Countless works have provided valuable insights into the chemical, ionization, and kinematic conditions of what is now called the circumgalactic medium. A new concept called the baryon cycle was birthed in which the balance of accretion modes, stellar feedback, gas recycling, and outflow dynamics of galactic gas was found to be closely linked to how baryons respond to dark matter halos of a given mass. Modern theory known as halo abundance matching has helped us empirically connect the average stellar mass to dark matter halos of a given mass. Powerful hydrodynamics simulations tell a story in which the average baryon cycle processes in a galaxy are closely linked to dark matter halo mass. In this chapter, we discuss how synthesizing both the observational data and theoretical insights has yielded a simple composite model of the baryon cycle.