The crime of fraud has been underdescribed and undertheorized, both as a wrong and as a legal prohibition. These deficits contribute to contention and uncertainty over the practice of punishing white-collar crime. This Article provides a fuller account of criminal fraud, describing fraud law’s open-textured, common law, and adaptive qualities and explaining how fraud law develops along its leading edge while limiting violence to the legality principle. The legal system has a surprising, often overlooked methodology for resolving whether to treat novel commercial behaviors as frauds: Courts and enforcers often conduct an ex post examination of whether an actor’s mental state included “consciousness of wrongdoing.” The Article summarizes this methodology’s history and contemporary applications before moving to the question of its justification. Among possible normative justifications for this unusual fault methodology, one fits best and involves the fewest complications: An actor’s pursuit of a novel course of conduct (that involves, as with all fraud, some deception causing or threatening harm), in the face of actual knowledge that prevailing norms reject that behavior, renders the actor equivalently blameworthy to an actor who intentionally pursues a course of conduct that the law has previously described as fraud. The Article concludes that ex post decisionmakers should continue to apply this methodology, despite its imperfections; that importing the methodology into fraud’s conduct rules would be possible but also perilous; and that the methodology identifies the subset of frauds for which criminal sanctions are justified if one purpose of sanctioning fraud is to assess blame.