The increasingly international reach of law owes part of its momentum to individual lawyers and law firms that function as carriers of ideas, processes and policies. U.S. lawyers are important participants in this expanding influence of law, both in the public sphere in areas such as human rights and in private areas, such as regulation of business. They work as representatives of both U.S. clients and foreign organizations and governments, bringing their basic mindset, shaped by education and practice experiences, into their dealings with foreign lawyers as they connect in a variety of roles, from co- and opposing counsel, to employees and partners. By working alongside and across the table from each other, U.S. and foreign lawyers have opportunities to influence one another and extend the reach of their conceptions about the way law and legal practice should work. Through these interactions, they define the terms of internationalization and thereby establish the agenda for the role of law at the international level. This article examines the regulatory environment in which that interaction occurs. It considers the obstacles faced by law firms intent upon combining foreign and U.S. lawyers and builds on prior work that investigated the impact on U.S. law firms of the development of an international market for legal services and the roles of foreign lawyers in the U.S. Regulation within the United States concerning the interaction between foreign and U.S. lawyers shapes the ways in which U.S. firms participate in the developing international market for legal services; it may well determine the placement and extent of that participation through U.S.-based activities. Further, restrictions on the interaction of foreign and U.S. lawyers limit the influence of U.S. practice and procedures on foreign lawyers, because such restrictions limit the opportunities for foreign lawyers to learn the ways and thinking of U.S. lawyers.