Stars and galaxies are born, evolve and die, but with lifetimes that are so long, we can only study snapshots that (in almost all cases) seem unchanging. In this chapter, we examine several techniques...Stars and galaxies are born, evolve and die, but with lifetimes that are so long, we can only study snapshots that (in almost all cases) seem unchanging. In this chapter, we examine several techniques for determining the ages and lifetimes of stars and then see how the Universe and its constituents evolve through cosmic time.