Because crime tends to run in families, many observers have assumed a genetic contribution to criminality can be identified. Evidence seems to show genetic factors are related to crime, as reflected by studies of family resemblances and intergenerational transfers, continuities in misbehavior, and twin and adoption cases. Studies also indicate that families influence the development of their offspring through social and physical placement and that child-rearing practices influence the development of young people and convey values. The author concludes genetic transmission of characteristics that contribute to risk for misbehavior, social environments that encourage toughness and antisocial actions, and child-rearing practices that legitimize the use of force have all been used to explain how families contribute to crime. The author indicates, however, that little is known about conditions in the environment that can ameliorate poor child-rearing or which types of child-rearing are most effective for different types of children. 138 references