 The Second Law of ordinary thermodynamics has a long, distinguished, and contentious history in the Twentieth Century debates about the philosophical foundations of physics, ramifying into virtually every important topic in the philosophy of physics in particular, and into many important topics in philosophy of science in general, including: the relation between thermodynamics and statistical mechanics; the Measurement Problem of quantum mechanics, and the status and meaning of theories of quantum information and computation; the definition of various arrows of time and the relations among them; the so-called Past Hypothesis in cosmology; determinism; causation; prediction versus retrodiction; the nature of reasoning based on idealization and approximation; emergence and reduction; and problems with theory confirmation. 