Over the last 25 years, there has been a sustained and highly productive surge of research on conduct disorder (CD), antisocial behavior, and juvenile delinquency. As indicated by the other papers in this issue, it is probably fair to say that we know more about this cluster of problems and disorders than about any other set of behavior problems affecting youngsters. In this paper, it will be argued that an increasing number of longitudinal studies of CD and juvenile delinquency accord in identifying sets of powerful antecedents for serious conduct problems. Although these antecedents are related in a life-course trajectory toward CD beginning well before school entry, they vary systematically in their number, topography, importance, and the situations in which they operate and in their potential malleability, as a function of the developmental level of the child. Although clinical treatment studies of children demonstrating well-developed CD have been disappointing, they provide promising leads for its prevention. It will be argued that by examining these leads within a developmental framework, clear implications for the next generation of prevention studies can be drawn. An attempt will be made to synthesize existing evidence from treatment and longitudinal studies to suggest comprehensive and theory-driven prevention strategies for CD at two phases of development: before and after the transition into elementary school.