Understanding criminal behavior as a biological or physiological phenomenon has continued in its ascendancy by advances made in the fields of genetics and neuroscience in understanding behavior. The development of criminal behavior is a biopsychosocial phenomenon, and factors that influence its development derive from multiple sources, ranging from genetic heritability to gang participation. Risk factors associated with the development of criminal behavior are found for each developmental phase, with the most significant risk factors for each developmental period being those that influence the achievement of developmental milestones. Thus, during infancy, factors that interfere with the formation of a secure attachment appear to be most detrimental while during adolescence, risks associated with peer relationships are critical. This chapter explores these biological and environmental risk factors and their effect on behavior across development. Given the individual and societal costs associated with antisocial behavior, the benefits of such an investment seem clear.