The over-exploitation of commonly-held resources is typically analyzed as an instance of market failure that calls for legislation to internalize the social costs that private activities impose on the environment. In this article, I argue that to the extent that this analysis ignores the regulatory effect of the common law, it is unsound. In The Tragedy of the Commons, Garret Hardin points out that there are two solutions to the tragedy: privatize the resource or restrict access to it. Environmental legislation is a means restricting access to the commons. The evolutionary development of common law is a means of privatizing the commons. These represent alternative methods of environmental regulation. Proper public policy analysis requires a comparative assessment of the efficacy of these methods for resolving any particular environmental problem. In many, if not most cases, such an assessment will show common law regulation to be superior to environmental legislation.