Much criminological research concentrates on offending throughout the adolescent years. In comparison, adult criminality has received relatively little attention. This is unfortunate because two issues relating to adult crime stand out as having significant implications for the future progress of criminological theory. The first issue is whether adult criminality and juvenile delinquency require different explanations. The second is whether desistance, or the winding down of criminal activity that takes place in young adulthood, requires an exegesis that stands apart from the onset of delinquent behavior in adolescence. Criminological theories generally fail to address these two issues, in part, because they lack a developmental perspective. That is, they do not focus on changing patterns of criminal involvement with age nor do they fully incorporate the many changes in personality, peer relations, family interactions, and life circumstances that take place throughout adolescence and adulthood. This essay examines theories of adult development and their potential applications to the etiology of adult criminality and processes of desistance.