This Article examines the debates over recent proposals for “mens rea reform.” The substantive criminal law has expanded dramatically, and legislators have criminalized a great deal of common conduct. Often, new criminal laws do not require that defendants know they are acting unlawfully. Mens rea reform proposals seek to address the problems of overcriminalization and unintentional offending by increasing the burden on prosecutors to prove a defendant’s culpable mental state. These proposals have been a staple of conservative-backed bills on criminal justice reform. Many on the left remain skeptical of mens rea reform and view it as a deregulatory vehicle purely designed to protect defendants accused of financial or environmental crimes. R...