We delineate the various ways in which rights to environmental and other resources can be assigned to individuals or groups. We then examine models of individual and group interactions, drawing out their implications for the ways in which resources will be utilized and managed under various rights assignments. Resources are classified into various groups (such as "collective" and "private") depending on the type of rights assignment that is most appropriate, and we critically examine situations in which it is claimed that certain combinations of rights and rules of behavior will lead to an "ideal" allocation of the associated resources. We argue that in all but a very limited set of circumstances, efficient allocations will require at the least some form of social intervention, and we discuss both formal and informal models of social organization toward this end. Various distortions are identified that may arise when incorrect assignments of rights are utilized. We discuss various practical ways of correcting for these distortions using instruments such as taxes, quotas, and markets for pollution permits.