In this text, the authors examine central issues in the development of criminal propensity through studies of life-course perspective and from criminal research involving biological and genetic factors. The authors trace the origins of criminality—that is, the propensity to violate social norms and rules—from conception through birth, through childhood, adolescence, and adulthood. The authors equally discuss biological and genetic research associated with criminality, as well as discuss research into specific environmental agents that cause, facilitate, or maintain criminal propensity.