Which undergraduate degree programs at the University of Colorado at Boulder enroll the most students? The answers might surprise you. The largest department at CU, based on spring figures, is psychology by a long-shot. Almost twice as many students study psychology - 1,446 - as the No. 2 major, communication. However, if the number of students in both the molecular (733) and environmental (719) biology departments are combined, biology gets the top spot at 1,452.