Rising college enrollment over the last quarter century has not been met with a proportional increase in college completion. Comparing the high school classes of 1972 and 1992, we show declines in college completion rates have been most pronounced for men who first enroll in less selective public universities and community colleges. We decompose the decline into the components due to changes in preparedness of entering students and due to changes in collegiate characteristics, including type of institution and resources per student. While both factors play some role, the supply-side characteristics are most important in explaining changes in college completion. (JEL I23)