This dissertation investigates the mutual life project of Signe (1896-1988) and Axel Höjer (1890-1974), a married couple who were key actors in the construction of the Swedish welfare state. It emphasises the ways in which they went about asserting a special public health expertise in different contexts. As starting points I take the malleability of the concept folkhälsa (people’s health or population health) and the centrality of expertise in the governance of modern societies. Theoretical concepts such as gender, policy transfer, biopower and governmentality are central to the analysis. The dissertation includes three parts. The first part investigates how the Höjers agreed to coordinate their work and how they, with reference to ideas picked up in France and England at the end of World War I, attempted to reform mother and child health care in Sweden. Their strategies where rhetorical but also practical, using Hagalund outside Stockholm as their experimental ground. The second part investigates, firstly, how Axel Höjer, as General-Director of the Medical Board of Sweden (1935-52) asserted a sociomedical expertise, integrating the emerging social sciences and universalist views on the organisation of the welfare state into the realm of medicine, in order to launch ideas of a thorough reorganisation and expansion of the Swedish health care system. His focus was on preventive medicine and health care, with the complete physical, mental and social health of the whole population as an explicit goal. Secondly, it explores how Signe Höjer at the same time tried to launch ideas on health and wellbeing as a social politician and a public committee member. She also tried to define family policy as a specific policy area. However, despite her training as a nurse and a social worker, she was largely confined to asserting a particularly ”female” expertise, which made her position rather ambiguous in terms of authority. The third part investigates how the Höjers, in the 1950s and 60s, worked with international health, Axel mainly for the WHO in India and Ghana, Signe as a policy entrepreneur, primarily in the fields of childcare and family planning. My findings partly confirm theories that see development aid as an extension of domestic social policy, but they challenge the view of aid as a simple one-way process. I demonstrate how the Höjers at least tried to adapt their projects abroad to meet local circumstances, and also show how they brought lessons from the third world to a domestic public. In the latter case they did not primarily act as experts of Swedish-style social policy, but as experts on the developing countries and on development aid.