This article explores the Ostroms’ perspective on nonprofit enterprises and on the place of the "third sector" within the broader ecology of governmental, for-profit, and nonprofit forms of social organization, focusing on three levels: the micro level based on a taxonomical analysis of the nature of (quasi)public goods and of the implications of their heterogeneity for their provision and consumption through nonprofit arrangements (with a special focus on the notion of "coproduction"); the mezzo level—the analysis of the various organizational structures emerging around (quasi)public goods dealt with by compounded units of production, provision, and consumption (with a focus on the notion of "public economy"); and the macro level—the introduction of the notion of "polycentricity" as a meta-framework inviting a reconceptualization of the relationships between the for-profit, nonprofit, and governmental organizations in diverse and dynamic institutional environments.