The neoclassical concept of the market is built on a number of assumptions that lead one to view it as a type of ether, devoid of any institutional content. In opposition to this point of view, this article proposes an alternative characterization of markets based on the fundamental principles of institutional and post-Keynesian economics. After reviewing the main features that characterize the behavior of economic agents, we analyze the set of interrelations between these agents within markets and the role of institutions in the regulation of these interrelations. Finally, we discuss some of the consequences generated by the institutional dimensions of markets with regard to their origins and evolution, the justification for their existence, or the evaluation of their results.