• This article reviews the literature on assortative mating for psychological traits and psychiatric illness. Assortative mating appears to exist for personality traits, but to a lesser degree than that observed for physical traits, sociodemographic traits, intelligence, and attitudes and values. Concordance between spouses for psychiatric illness has also been consistently reported in numerous studies. This article examines alternative explanations for such observed concordance and discusses the effects of assortative mating on population genetics and the social environment.