This article reviews behavioral-genetic research into human antisocial behavior. The focus is on studies of antisocial behavior that have been leading the way in investigating environmental and genetic influences on human behavior. The first generation of studies, which provided quantitative estimates attesting that genes and environments each influence about half of the population's variation in antisocial behaviors is interpreted. Then how behavioral-genetic methods are being applied to test developmental theory and to detect environmental causes of antisocial behavior is illustrated. Evidence for interactions between genes and the environment in the etiology of antisocial behavior is also examined. The article ends by envisioning future work on gene-environment interplay in the etiology of antisocial behavior. © 2005 Elsevier Inc. All rights reserved.