This chapter has three objectives: the clarification of the nature of the marketing firm as a source of marketing-based intermediation between suppliers and consumers, the portrayal of the marketing firm as a contextual system (in terms of bilateral contingency and metacontingency), and its further portrayal as an embodiment of collective intentionality. These considerations allow the incorporation of the theory of the marketing firm into the overarching philosophy of economic psychology that is intentional behaviourism. It first pursues the raison d’être of the marketing firm in terms of its intermediating between the essential economic and social actors who are vital to the formation and operation of markets and contrasts this conception of the marketing firm with those of Spulber and Coase. The chapter, therefore, enhances the theory of the marketing firm by examining it within the philosophical framework of intentional behaviourism, which is concerned with the proper use of cognitive explanation in the study of socio-economic behaviour. The marketing firm may be considered as either a contextual system or an intentional system. The theory of the marketing firm was conceived within a broadly behaviourist paradigm, but there are reasons to turn to an account of corporate action that reflects perception and cognition. This is especially apposite, for instance, in the consideration of entrepreneurial behaviour. This progression parallels the development of the theory of consumer choice which incorporates successive stages of interacting extensional and intentional analyses. The first stage employs behaviourist models, which are supplemented with intentional explanations if and when they have proved inadequate. The aim is not to supersede the behaviourist model but to enhance it when necessary. This research strategy is here introduced in the context of the theory of the marketing firm through consideration of such extensional research frameworks as bilateral contingency analysis and metacontingency analysis, which are closely linked to behaviourist modelling, and collective intentionality, which relies on cognitive reasoning. This necessitates viewing the marketing firm, first, from the perspective of a contextual system and, secondly, as an intentional system.