Abstract: Galaxies are remarkably diverse in their properties, ranging from irregular to disky to elliptical in morphology, and from blue to red in color. At the same time, when analyzed systematically, galaxy populations exhibit striking regularities, with clear trends with mass and redshift. How does this "regular complexity" emerge from the hot Big Bang? I will present results from the FIRE simulations which shed some light onto the processes that shape galaxies. The FIRE zoom-in simulations resolve the multiphase interstellar medium of galaxies and model several different feedback processes (including Type II/Ia supernovae, stellar winds, and radiation) while including the cosmological environment. I will highlight recent results on the formation of disk galaxies, the "burstiness" of star formation, and galactic winds. Our new results indicate that transitions in each of these important phenomena can be simultaneously explained by a phase transition in the inner circumgalactic medium, "inner CGM virialization" (ICV), and arise from the interplay between feedback energy produced on small scales and the physics of halo gas on larger scales.