The relationship between interpersonal trust and membership in voluntary associations is a persistent research finding in sociology. What is more, the notion of trust has become a central issue in current social science theorizing covering such diverse approaches as transaction costs economics or cognitive sociology. In different ways and for different purposes, these approaches address the role of voluntary organizations, although, as this paper argues, much of this thinking remains sketchy and underdeveloped. Against an empirical portrait of this relationship, the purpose of this paper is to assess such theorizing. We first set out to explicate major approaches to trust in economics, sociology and political science, using the non-profit or voluntary organization as a focal point. We then examine the various approaches in terms of their strengths and weaknesses, and, finally, identify key areas for theoretical development. In particular, we point to the social movement literature, the social psychology of trust, and recent thinking about civil society.