This project studies the collaboration and exchanges in population and family policy between population associations in Finland and Sweden in the 1940s. Investigating the mobilization on family policy issues during this period, the project analyses how considerations regarding population, family and procreation were transferred and negotiated in national and transnational contexts. The research question concerns what I call transnational pronatalism or how pronatalist principles – i.e. ideals and efforts to support nativity – were uttered, staged, motivated, communicated, negotiated and mobilized around as part of transnational exchanges. The object of study is the interaction and exchanges between three organizations in Finland and Sweden established in the early 1940s with the aim to increase nativity by promoting positive family values and supporting the interests of families with many children, i.e. organizations usually labelled as “pronatalist”. The project asks how collaborations to promote population, family and procreation were possible when they on the one hand were performed over national borders and on the other hand were based within national contexts where some issues are more pressing than others. By exploring this question historically, using methods from conceptual history, the overarching purpose of the project is to historizise the concept prontalism.