Recent studies have directed attention to the nature of romantic involvement and its implications for offending over the life course. However, this body of research has overlooked a defining aspect of nonmarital romantic relationships: Most come to an end. By drawing on insights from general strain theory, the age-graded theory of informal social control, and research on delinquent peer exposure, we explore the impact of romantic dissolution on offending and substance use during late adolescence and emerging adulthood. Using data from the 1997 cohort of the National Longitudinal Survey of Youth, we arrive at three general conclusions: 1) Experiencing a breakup is directly related to a range of antisocial outcomes; 2) the effect of a breakup is dependent on post-breakup relationship transitions; and 3) a breakup is associated with increases in offending and substance use among males and in substance use among females. We conclude with a discussion of the implications of our findings for the future of research on romantic involvement and crime over the life course.