This monograph places the science and ideology of eugenics in early twentieth century Portugal in the context of manifestations in other countries in the same period. The author argues that three factors limited the impact of eugenics in Portugal: a low level of institutionalization, opposition from Catholics and the conservative nature of the Salazar regime. In Portugal the eugenic science and movement were confined to three expressions: individualized studies on mental health, often from a ‘biotypological’ perspective; a particular stance on racial miscegenation in the context of the substantial Portuguese colonial empire; and a diffuse model of social hygiene, maternity care and puericulture.