It has become commonplace in management research to refer to "transaction cost theory," a joint Coase–Williamson approach to economic organizing. This off-the-cuff usage overlooks their differences by treating Coase as a pre-Williamsonian. I argue that their theoretical frameworks are different, and that they use different theoretical assumptions leading to different views of transaction costs, markets, and the firm. These differences are wide enough that they should be considered two distinct theoretical approaches to the firm. I outline their differences and elaborate on the implications of reconsidering Coase's distinct theory for management and strategy research.