This article examines the factors that determine a high school's probability of offering Advanced Placement (AP) and International Baccalaureate (IB) courses. The likelihood that a school offers advanced courses, and the number of sections that it offers, is largely driven by having a critical mass of students who enter high school with eighth-grade test scores that are far above average. The number and qualifications of the instructional staff, in contrast, play a very small role. The results suggest that the willingness of schools to offer advanced courses is driven by real, perceived, or created student demand and that there may be few resource constraints that prevent schools from supplying advanced courses. (Contains 3 figures, 4 tables, and 11 notes.)