I will discuss insights from analytic and numerical models of galactic chemical evolution and observations of Milky Way elemental abundances from the SDSS APOGEE surveys. Under generic assumptions, the abundances and abundance ratios in fully mixed one-zone chemical evolution models approach an equilibrium in which element production is balanced by depletion of heavy elements by star formation and outflows. A stellar population can be metal-poor either because it has not yet evolved to equilibrium or because high outflow efficiency makes the equilibrium abundance itself low. Sudden transitions in a system can produce temporary boosts in alpha-to-iron ratios and other surprising behavior such as backward evolution of a stellar population from high metallicity to low metallicity. I will discuss applications of these ideas to understanding the distribution of stars in (alpha,iron,age)-space through the Milky Way disk, the origin of scatter in abundance ratios and dimensionality of the stellar distribution in chemical abundance space, supernova yields, and whether the Milky Way has a galactic wind at the present day.