Our current view of galaxies considers them as systems of stars and gas embedded in extended halos of dark matter, much of it formed by the infall of smaller systems at earlier times. Star formation within galaxies affects the surrounding gas through primary forms of astrophysical feedback (mass, energy, radiation, metals). Both semantic and physical issues remain. Are the edges of galaxies defined by gravity or by gas outflows? When does gas cease to be the circumgalactic medium (CGM) and become part of the intergalactic medium (IGM)? I will discuss observational and theoretical work relevant to galaxy halos, IGM metallicity evolution, and CGM/IGM studies with the Cosmic Origins Spectrograph on the Hubble Space Telescope. As cosmological simulations become more advanced, their prescriptions for feedback from quasars and star-forming galaxies will need more sophistication in how they treat the injection of mass, heavy elements, ionizing radiation, and energy.