This essay undertakes two tasks: first, to describe the differing mens rea requirements for accomplice liability of both Anglo-American common law and the American Law Institute's Model Penal Code; and second, to recommend how the mens rea requirements of both of these two sources of criminal law in America should be amended so as to satisfy the goals of clarity and consistency and so as to more closely conform the criminal law to the requirements of moral blameworthiness. Three "pure models" of the mens rea requirements for complicity are distinguished, based on the three theories of liability conventionally distinguished in the general part of Anglo-American criminal law. One of these, the vicarious responsibility model, is put aside initially because of both its descriptive inaccuracy and its normative undesirability. The analysis proceeds using the other two models: that of the mens rea requirements for principal liability for completed crimes, and that of the mens rea requirements for attempt liability. Both the common law and the Model Penal Code are seen as complicated admixtures of these two models, the common law being too narrow in the scope of its threatened liability and the Model Penal Code being both too broad and too opaque in its demands for accomplice liability. The normative recommendation of the paper is to adopt the model for the mens rea of complicity that treats it as a form of principal liability, recognizing that the overbreadth of liability resulting from adoption of that model would have to be redressed by adopting a "shopkeeper's privilege" as an affirmative defense separate from any mens rea requirement.