U.S. agencies routinely base their domestic regulations on international considerations, such as the benefits of coordinating American and foreign standards or the foreign policy advantages of a particular policy. I refer to this phenomenon as the internationalization of agency actions. This Article examines what the internationalization of agency actions means for agency decision-making processes, institutional design, and legal doctrine. It creates a stylized model of how agencies determine whether to coordinate their standards with foreign regulations. Among other institutional design findings, it shows that court opinions that reduce the stringency of judicial review when agencies implement internationally coordinated standards make such coordination more likely to occur, but they simultaneously deprive the executive of bargaining power because U.S. agencies cannot credibly threaten that any coordinated agreement must align more closely with U.S. values or risk being overturned in U.S. courts. This Article also develops a taxonomy of international factors relied on by agencies and applies that taxonomy to help clarify the doctrinal issue of whether and when agencies can use international factors to justify their actions in court. This taxonomical approach shows how the Supreme Court’s opinion in Massachusetts v. EPA can reasonably be read to allow agencies to invoke a far broader range of foreign policy rationales than some prevailing views suggest.