The environmental laws create a complex regulatory system affecting a wide range of economic activity in the United States. Given the wide range of potential environmental violations, it might have been preferable for Congress to specify which environmental violations could result in criminal prosecution. Instead, Congress made only limited distinctions between acts that could result in criminal, civil, or administrative enforcement. If the same violation often could give rise to criminal, civil, or administrative enforcement—and if mental state requirements only preclude criminal enforcement for a small subset of violations—what determines which environmental violations result in criminal prosecution? The answer is the exercise of prosecutorial discretion, which exists in all areas of the criminal law, but assumes a particularly critical role in environmental cases because so much conduct falls within the criminal provisions of the environmental laws.