This contribution is based on an extensive literature review of student dropout in Europe, which was carried out by a research group of the Danish Clearinghouse for Education in cooperation with an international expert group in 2012/2013. The review served to answer three basic questions: What is dropout? Why does it occur? What can be done to reduce or prevent it? Only empirical studies were included in the review and altogether 44 studies were included. The article points out that student dropout is a more complex and multidimensional issue than most people think and that it is important to distinguish between formal dropout (i.e., leaving university studies altogether before degree completion) and transfer (i.e., changing subject and/or institution). The review summarizes and discusses the main results of the 44 studies included in terms of nine dimensions: (a) study conditions at university, (b) academic integration at university, (c) social integration at university, (d) personal efforts and motivations for studying, (e) information and admission requirements, (f) prior academic achievement in school, (g) personal characteristics of the student, (h) sociodemographic background of the student, and (i) external conditions. The conclusions provide an answer to the three questions posed above and include recommendations for further research, university leadership, and policymakers.