This essay explores the detailed argument of the Coase Theorem, as found in Ronald Coase’s “The Problem of Social Cost” and subsequently defended by Coase in The Firm, the Market, and the Law. Fascination with the Coase Theorem arises over its apparently unassailable counterintuitive conclusion that the imposition of legal liability has no effect on which of two competing uses of land prevails, and also over the general difficulty in tying down an unqualified statement of the theorem. Instead of entering (...) the debate over what exactly the theorem holds, this article suggests that the core of Coase’s reasoning is flawed and to the extent that any version of the theorem relies upon this reasoning it can be disproved. It is further suggested that a version of the theorem which avoided the need for Coase’s core argument by focusing on “the efficiency thesis” at the expense of “the invariance thesis” would be insufficiently significant to merit the status of a theorem; and that, in any event, Coase’s reasoning does not sustain an efficient outcome. The heart of the essay comprises the allegation of an error made by Coase when he transferred his core argument to the context of economic rents. The essay commences by considering and modelling the nature of the counter-intuitive thrust to the Coase Theorem, which is used to trace the development of Coase’s reasoning, and ultimately to expose the flaw it contains. Ancillary observations are made on the relationship between the Coasean analysis of characteristically legal problems and the conditions of general market equilibrium, and the theoretical status of law-and-economics. (shrink)