This article explores whether transnational corporations or their executives can be held criminally or civilly liable for aiding and abetting human rights violations committed by governments, militaries or other actors in foreign countries where they do business. The article particularly examines the mens rea element under international law: whether the aider or abettor must knowingly—or instead purposefully—assist the principal to commit a crime. At present, the principal concern of major corporations about liability for aiding and abetting is the risk of being held liable in U.S. courts under the Alien Tort Statute. But whatever happens with ongoing ATS litigation, the issue of aiding and abetting may become more important in the future in other contexts - including the International Criminal Court, national courts in the home countries of major corporations, and national courts in developing countries where large companies do business. If the standards were clarified for aiding and abetting, and especially for the mens rea element, the resulting legal certainty would be fairer for both corporate managers and victims of human rights violations, while avoiding needless sources of friction among states. As aiding and abetting liability evolves for corporate actors, several principles of international law should be borne in mind. First, even if corporations per se cannot be prosecuted before international criminal tribunals, corporate executives have long been subject to international criminal jurisdiction. Second, international criminal law has long recognized criminal responsibility for aiding and abetting. Third, international law recognizes that civil liability of corporations is widely accepted by national justice systems. Fourth, international law increasingly encourages states to hold corporations criminally responsible for aiding and abetting violations of international law. Combining these principles, whatever may have been the status of corporate aiding and abetting liability in the apartheid era, international norms against corporate aiding and abetting of violations of international criminal law are now widely accepted internationally.