This paper explores the potential of sociology to fill certain gaps in economic theory. It examines in particular its capacity to explain: 1) the institutional supports required to make a competitive market work; and, 2) the limits of the assumption of rational choice behavior. The dominant sociological approach to problems of this kind is to postulate the existence of different social realms, but it does not have a strong theory of how these realms come into existence and how their boundaries come to be defined. Its failure to provide such a theory is particularly limiting because the salient characteristic of the period in which we are living is fluidity of boundaries, the boundaries of the firm and the family no less than the boundaries between the economic and social realms themselves. The paper concludes with suggestions for how a theory of boundary formation could be built around a notion of ?interpretation? as a mode of human behavior distinct from rational choice but co-existing with it.