This book focuses on the apparently surprising convergence between anarchism and eugenics. By tracing the reception of eugenic ideas within five different anarchist movements –Argentina, England, France, Portugal and Spain – the book argues that, in fact, there is ample evidence for anarchist interest in, and implementation of, some form of eugenics. The author argues that this intersection between anarchism and eugenics can be understood as an emanation from anarchism’s nineteenth-century legacy, which harnessed science as a means to change the social world and an ideological commitment to voluntarism as a political praxis. Through the articulation of interest in birth control, ‘neo-Malthusianism’, freedom to choose for women and revolutionary objectives, many anarchists across these five countries provided the basis for the creation of ‘anarchist eugenics’ in the early twentieth century.