The principles of legality and separation of powers are conventionally understood to require that law-making, law- interpreting, and law-enforcement be carried out by separate institutions. This paper challenges this understanding in the context of federal criminal law. Descriptively, it maintains that federal criminal law is most accurately conceptualized as a "common-lawmaking" regime in which Congress delegates power to courts by enacting incompletely specified statutes. Normatively, it argues that the law would be better if the delegated-lawmaking authority that courts now exercise were instead wielded by the Department of Justice. The legal mechanism for this reform would be the so-called Chevron doctrine, which requires courts to defer to Executive Branch readings of ambiguous regulatory statutes. The likely advantages of such an arrangement include greater expertise in the making of criminal law, greater uniformity in the interpretation of it, and (most surprisingly) greater moderation in the enforcement of it.