Editors' Summary: Congress gave private citizens an important, though secondary, role in enforcing the new pollution control statutes of the 1970s. EPA and the states were given the principal responsibility to act when polluters violated standards, but the public was not expected necessarily to sit back and wait for the governments to solve the problems. Citizens could take enforcement matters into their own hands if the governments failed to act. The primacy of government enforcement was recognized in provisions requiring citizens to notify state agencies and EPA of their plans to file enforcement actions and to take a back seat if the agencies diligently prosecuted enforcement cases "in court." To date, one of the major issues raised in citizen enforcement cases is the effect on such citizen cases of administrative enforcement action. State and federal agencies' preferred enforcement route has been administrative, not judicial. Can administrative enforcement bar citizen suits? The authors examine this question in the context of the legislative history of the Clean Air and Clean Water Acts, and conclude that Congress intended that administrative enforcement action may suffice to preclude citizen suits.