Traditionally, economists have viewed social relations as friction or impediments to exchange and have excluded social relations from their analyses by assuming autonomous actors. Recently, however, a number of scholars - economists, sociologists, anthropologists, and other social scientists - have begun to discuss the numerous ways in which social arrangements both prompt and channel economic activity. Rational choice theory, social capital and network analysis, and agency and game theory, are among those approaches that consider the effects of social relations on economic action. In this paper, that discussion is extended by arguing that social relations can function as collateral or assurance that an economic transaction will proceed as agreed by the parties involved. Recent microeconomic theories are reviewed and how They might be developed following this observation, which is derived from sociological and anthropological studies of economic action and organizations.