This chapter first reviews some prominent models of dropping out and the role that individual factors, including engagement, and contextual factors play in the process. It then reviews empirical research related to those factors, with a focus on engagement-related factors. Scholars have proposed a number of models to explain the process of dropping out of school. While there is a fair amount of overlap in the models, they differ with respect to the specific factors that are thought to exert the most influence on dropping out and the specific process that leads to that outcome. The review of conceptual models of the empirical research literature leads to several conclusions about why students drop out. First, no single factor can completely account for a student’s decision to continue in school until graduation. Just as students themselves report a variety of reasons for quitting school, the research literature also identifies a number of salient factors that appear to influence the decision. Second, the decision to drop out is not simply a result of what happens in school. Clearly, students’ behavior and performance in school influence their decision to stay or leave. But students’ activities and behaviors outside of school—particularly engaging in deviant and criminal behavior—also influence their likelihood of remaining in school. Third, dropping out is more of a process than an event.