This article aims to increase the knowledge of the roles and functions of public health institutes (PHIs) by exploring and comparing the Scandinavian PHIs, their roots, and developments over time. The research questions are the following: What was the history behind these public institutions? How have they changed over time? Have they followed divergent or parallel paths of change? How, if at all, have they been influenced by public sector reforms? Comparing the three Scandinavian countries based on an institutionalist approach, the article seeks to increase the understanding of the role of PHIs in governing public health. The article is based on documents from parliaments and governments from the public health institutes, supplemented by institution narratives and relevant public health and public administration literature. The Scandinavian PHIs have common roots from the early 1900s, have followed different routes, and have different institutional characteristics and different roles as public health institutions. However, after more than 100 years, the Scandinavian PHIs belong to the international PHI organization. They are responsible for knowledge dissemination, surveillance, and preparedness for the handling of epidemics and pandemics. The article argues for more comparative research on institutions related to public health authorities, such as the PHIs.