Recent emphases on reciprocity, bilateralism, retaliation, and regulatory restrictions (e.g., pollution, health, and safety standards) in US trade policy have been viewed as serious threats to the liberalization of international trade which characterized the post-World War II period. This paper explores a different interpretation, arguing that the bilateralism, reciprocity, and regulatory standards which have been viewed as moves toward protectionism can also be seen as mechanisms for dealing with the enforcement problem inherent in trade agreements in the presence of costly negotiation, costly enforcement, and strong protectionist constituencies. Trade policy among large economies has aspects resembling a ‘prisoners' dilemma’ because each country has an incentive to engage in opportunistic behavior by reneging on its commitments to liberalization. In the absence of effective third-party enforcement, a ‘self-enforcing agreement’, which through its terms automatically imposes substantial costs on any party guilty of noncompliance, may be one viable means of enforcement. Reciprocity, bilateralism, and regulatory standards can serve to facilitate self-enforcing agreements.