The International Baccalaureate Diploma Program (IBDP) is an advanced- course program for students in high school. The program is offered throughout the world, but has seen particular growth in the United States, where it expanded rapidly over the last 15 years, from nearly 300 to about 900 schools, a more than 200 percent increase. Despite its rapid U.S. expansion, little is known about the role of program in the U.S. educational system, and its growth, as a whole. This was due, in part, to previous data limitations; one outcome of this project is a longitudinal dataset of IBDPs in the U.S. (described in Chapter 2). As the program continues to grow and expand as an advanced educational option in much of the country, my dissertation fills a gap in the current literature by describing where the program fits in the U.S. educational landscape and why its recent growth is consequential – both in shaping educational opportunity, the landscape of advanced course taking more broadly, and in effectively maintaining inequality. I apply allocation and stratification theories of the sociology of education, which have largely focused on individual outcomes and achievement, to examine the growth and expansion of IBDP – noting broad-level trends in where the program is located, how quickly the program expanded in the U.S. (Chapter 3), and the access different groups have to the program (Chapters 4 and 5). Previous work in this area has largely taken place at the student level, focusing on student achievement and the sorting of students as a function of prior test scores, teacher evaluations, and socio- demographics. While still attending to issues of access and stratification, I extend this literature to examine these issues at the school, school district, and national levels.Drawing on neo-institutional theories, I contextualize the program's growth as co-occurring with standards-based accountability policies and calls to democratize advanced courses. I then analyze the extent to which the program contributes to racialized tracking with second-generation segregation in the U.S., finding that schools in districts under desegregation orders have a higher predicted probability of racially tracking students in IBDP, hyper-segregating White students in, and Black students from, the program. Finally, motivated by the literature on educational expansion and effectively maintained inequality, I examine the characteristics of school districts offering and implementing IBDP.