Developmental and life-course criminology (DLC) focuses on the development of offending and antisocial behaviour, the importance of risk and protective factors, and the effects of life events. The ICAP theory specifies risk and protective factors that influence the development of long-term antisocial potential (varying between individuals) and situational factors that influence short-term antisocial potential (varying within individuals over time). It also specifies the cognitive processes that influence whether the antisocial potential (AP) becomes the actuality of offending in any situation, and the consequences of offending that have feedback influences on AP. This chapter describes a detailed empirical test of the ICAP theory based on the Cambridge Study in Delinquent Development (CSDD), which is a prospective longitudinal survey of 411 South London males beginning at age 8. It also discusses some research and policy implications of the ICAP theory and of the results of the empirical test.