The topic of undergraduate academic engagement has been a matter of intense inquiry for more than a generation. This paper examines the other side of the coin: the size and characteristics of academically disengaged populations. Drawing on classic sociological work on conformity and deviance, we theorize four dimensions of student academic disengagement: values disengagement, behavioral disengagement, alternative involvement, and interactional disengagement. Using survey data, we estimate the size of disengaged populations along each of these dimensions and the characteristics of students who are more likely to be found among disengaged populations. In this sample of students from a selective public research university system, the size of the disengaged population varies between 10 and 25 percent, depending on the measure used. Male students, students with low college GPAs, and students in the arts, humanities, and social sciences were more likely to be found among disengaged populations. We conclude by proposing treatments for disengagement attuned to each of the four dimensions and to these disengagement-prone populations.