Sanctions for illegitimacy vary enormously across cultures and are linked to social structure. Some societies handle non-marital births in a relaxed way; others use restitutive sanctions; and others repressive sanctions. This study of 122 non-industrial societies shows that the regulation of illegitimacy is more varied than any particular theory suggests (and there are many, including Marxism, functionalism, sociobiology, and feminism). The work aims to test a variety of theoretical ideas about the possible factors involved in social regulation of illegitimacy -- social hierarchy, fraternal interest groups, female power, extended family structure, affection for children, and father involvement with infants -- and to examine combinations of these factors for predictive power. This study will be of interest to scholars and students in sociology, family studies, and cultural anthropology.