Protection of common natural resources is one of the foremost challenges facing our society. Since Garrett Hardin published his immensely influential The Tragedy of the Commons, theorists have contemplated the best way to save common-pool resources—national parks, fisheries, heritage sites, and fragile ecosystems—from overuse and extinction. These efforts have given rise to three principal methods: private ownership, community governance, and use restrictions. In this Essay, we present a different solution to the commons problem that has eluded the attention of theorists: access rationing. Access rationing measures rely not only on restrictions on the number of users but also on a variety of economic, informational, and technological techniques that can be readily adjusted to changing circumstances. By focusing on the point of entry, access rationing prevents harm to natural resources from arising ab initio. Furthermore, access rationing offers the twin virtues of simplicity and flexibility. Finally, access rationing has the additional advantage of transparency, as it allows members of the public and nonprofit organizations to monitor the performance of regulatory agencies. Drawing on a myriad of real-world examples, the present Essay is the first to provide a comprehensive theory of access-based measures for governing the commons.