Eugenics arose at a crucial juncture in terms of demography (with the declining birth rate) and morbidity (with the shift to chronic diseases) in the later nineteenth century. These, in turn, shaped public measures in the early twentieth century. This chapter will examine eugenic concepts of population health, and how these entered public health concepts and practices. It will review the theoretical writings of Galton in Britain, and Schallmayer and Ploetz in Germany. Their theoretical writings provided fundamental concepts of how population health could be sustained in the emergent welfare state. Eugenics became a norm embedded in public health concepts, structures and interventions. The chapter will consider eugenic ideals and how these were to be sustained by such measures as health examinations prior to marriage, family welfare support and restriction of immigration. Eugenicists demanded comprehensive measures to promote the fit and healthy, and segregate the degenerate. I will consider the historiography of eugenics and its limitations as regards public health, as well as the implementation of actual health measures regarding a range of ‘racial poisons’ such as alcohol, tuberculosis and sexually transmitted diseases. Wider issues raised are those of the dissemination of eugenic ideas as well as the role of eugenically minded experts as guardians of national health.