In the conventional theory of common-pool resources, participants do not undertake efforts to design their own governance arrangements. Substantial empirical evidence exists, however, that many common-pool resources are self-governed. Thus, in this chapter, I briefly review the conventional theory of common-pool resources. Then, I provide an overview of the empirical studies that test this theory in experimental laboratories. In the third section, I provide an overview of the empirical studies of this theory conducted in field settings. Since research in the lab and in the field both provide evidence that appropriators from common-pool resources do self-organize, the fourth section is devoted to the presentation of an initial theory of self-organization focusing on the benefit-cost calculus of individual appropriators. Two major theoretical puzzles remain, having to do with the effect of the size of a group and its heterogeneity.