Gravitation, thermodynamics and quantum theory

During the past 30 years, research in general relativity has brought to light strong hints of a very deep and fundamental relationship between gravitation, thermodynamics and quantum theory. The most striking indication of such a relationship comes from black hole thermodynamics, where it appears that certain laws of black hole mechanics are, in fact, simply the ordinary laws of thermodynamics applied to a system containing a black hole. This paper will review the present status of black hole thermodynamics and will discuss some of the related unresolved issues concerning gravitation, thermodynamics and quantum theory.