  Statistical mechanics was the first foundational physical theory in which probabilistic concepts and probabilistic explanation played a fundamental role. For the philosopher it provides a crucial test case in which to compare the philosophers' ideas about the meaning of probabilistic assertions and the role of probability in explanation with what actually goes on when probability enters a foundational physical theory. The account offered by statistical mechanics of the asymmetry in time of physical processes also plays an important role in the philosopher's attempt to understand the alleged asymmetries of causation and of time itself. 