Abstract
The fates of "transboundary" environmental systems depend on how nation states interact with one another. In the absence of a hegemon willing and able to coerce other states into avoiding a "tragedy of the commons," shared environments will be safeguarded if international cooperation succeeds and degraded or even destroyed if it fails. Treaties and related institutions of international law give form to these efforts to cooperate. Often, they implore states to act in their collective (as opposed to their national) interests. Sometimes, they impel cooperating states to punish free riders. A few agreements coordinate states' behavior. Here, I present simple game-theoretic models showing whether and how treaties and related institutions can change incentives, aligning states' self-interests with their collective interests. I show that, as a general matter, states struggle to cooperate voluntarily and enforce agreements to cooperate but that they find it relatively easy to coordinate actions. In some cases, the need for coordination is manifest. In other cases, it requires strategic thinking. Coordination may fall short of supporting an ideal outcome, but it nearly always works better than the alternatives.