Editors' Summary: In this second of a three-part series, the authors examine the knowledge element in environmental crimes. They point out that while mens rea—or "guilty knowledge"—is a required element of most criminal offenses, a distinguishing feature of environmental crimes is that they require minimal proof of knowledge to sustain a conviction. In analyzing environmental crimes as general intent offenses, the authors first describe the public welfare offense doctrine, under which courts have interpreted the term "knowingly" to require only general awareness that a defendant was dealing with a substance likely to be regulated and knowledge that the conduct constituting the offense occurred. They contrast cases interpreting the knowledge elements of nonenvironmental statutes, which generally require proof of actual knowledge of illegality. The authors then survey significant decisions construing the knowledge element in environmental crimes, focusing on what the defendant must know about applicable legal requirements and the conduct in question. In particular, they analyze the intent element for permit offenses. Next, the authors discuss methods of proving knowledge for corporate and individual defendants, including direct and circumstantial evidence. The authors discuss in detail how prosecutors use the responsible corporate officer doctrine to impose liability on individuals at high corporate levels. Finally, the authors analyze the effectiveness of litigation strategies that focus on the difficulties regulated persons and entities face in understanding the complex environmental regulatory schemes under which they operate.