The validity of the laws of classical black hole mechanics, the existence of the Hawking effect, and the apparent validity of the generalized second law of thermodynamics have established beyond any reasonable doubt that a deep relationship exists between black holes and thermodynamics. Yet, some major issues remain unresolved, such as whether the entropy of a black hole should be viewed as "residing" in its deep interior, on its horizon, or in its "thermal atmosphere". I will review some of the main established results in black hole thermodynamics and discuss some of the open issues.