Forty years ago, Jacob Bekenstein and Stephen Hawking showed that black holes are "hot," with characteristic temperatures and entropies that depend on properties of their event horizons. The Hawking temperature and the Bekenstein-Hawking entropy are quantum and gravitational -- they depend on both Planck's constant and Newton's gravitational constant -- and, in fact, they provide one of the very few pieces of information about quantum gravity that we really believe with any confidence. Black hole thermodynamics hints at intriguing features of quantum gravity, such as "holography," the possibility that the fundamental physical properties of a finite region might be entirely described by quantum states at its boundary. But black hole thermodynamics is also surprisingly universal: that is, there seem to be many different approaches to quantum gravity that all give the same answers. In this talk, I will discuss the open question of what, if anything, we can learn about the fundamental properties of quantum gravity by studying black holes.