Background/Context: In the past 35 years, the International Baccalaureate Diploma Program has spread to 483 schools across the United States, with an ever-growing share of these schools located in the inner city. These American school sites comprise vastly different contexts than those in which the IB program began-the international schools of Europe. Purpose/Objective/Focus of Study: To understand the migration of the IB from international schools to inner-city schools, I examine both the intentions and the implementation of two of the most distinctive features of the program: its assessment system and its emphasis on promoting intercultural competence. Research Design: In this analytic essay, I rely on historical accounts to uncover the first principles that the founders sought to embed in the design of these two curricular components. Drawing on accounts written by journalists and educators about the implementation of the IB, I then consider implications of these first principles in the context of American schools generally, and inner-city schools in particular. Conclusions/Recommendations: I argue that although the growth of the IB may be due to the broad appeal of its first principles, as the IB continues to spread to new school sites, these first principles remain vulnerable, challenged by the constraints and conventions of the American schooling system. To remain true to its founding ideals and first principles, the program will need to continue to balance interests that in the American context often conflict, such as progressive and standards-based education, and access and prestige.