Environmental Management Systems (EMSs) offer an approach to regulatory policy that lies somewhere between free-market and traditional command-and-control methods. Worldwide, hundreds of thousands of private firms have adopted or are considering adopting these internally managed systems for improving environmental performance. In the United States, the Environmental Protection Agency has established a special recognition for firms that adopt EMSs. Already, numerous state agencies have proposed or adopted 'green-tier systems' that allow firms with EMSs to be exempted from otherwise applicable...