Over the past two decades the role of private parties in the policing of environmental regulation has grown dramatically. In some cases the Environmental Protection Agency (EPA) has led this effort. In other situations, private parties have provided the impetus for new policing activities that are conducted independently from the EPA. Private policing can be beneficial when the increased involvement of the private sector either decreases the costs of achieving a particular level of environmental performance or increases environmental performance in a cost-effective manner. Private parties, however, could also divert regulated entities away from regulatory objectives. This Article explores the privatization of environmental enforcement by presenting six examples and highlighting their benefits and costs. Although the examples cited are not necessarily representative of all private policing, their mixed results regarding the effectiveness of private sector participation shows a need for careful evaluation of these initiatives. The Article concludes by making a case for a more deliberate approach to evaluating the role of the private sector in the enforcement of environmental regulation, and suggests that before responding to continuing calls to further privatize environmental regulation and enforcement it is first necessary to ensure that existing private participation is helping to achieve regulatory goals.