This article analyses the institutional coevolution of policy sectors – in other words, the mutual influence and adaptation of the institutional connection between related policy areas. The article proposes a two-dimensional analytical space ranging from separation to unity on one axis and from superiority/subaltern to equality on the other. The article argues that the overall governance framework behind the coevolving sectors affects the institutional relationship between the sectors. In its empirical part, the article focuses on the healthcare and public health sectors. Based on a comparative historical examination of three countries with different healthcare systems – Australia, Germany, and the United States – the article shows that healthcare and public health coevolve differently depending on the type of national healthcare system. Further research can transfer the concepts introduced in this article to the analysis of other policy challenges, such as immigration or environmental protection.