A four-year state university system. California operates three separate public systems for postsecondary education: two-year community colleges, the four-year California State University (CSU) system, and the most selective University of California (UC) system. There are 23 CSU campuses serving more than 400,000 students. CSU generally accepts the top one-third of high school graduates and all qualified community college transfers. Eligibility for high school seniors to enter either CSU or UC is based on the completion of 15 one-year college prep courses (referred to as a-g courses), high school grades, performance on college entrance exams, advanced coursework taken, and personal attributes.