Research institutes, here defined as organizations involved in research and development but outside of the higher education sector and often in close cooperation with users, are found in most countries but not very well understood. This paper argues that institutes can be considered “hybrid organizations”, caught in between dichotomous cultural spheres with differing values. To retain their hybridity and to survive in the long run, research institutes need to create and sustain organizational legitimacy by establishing congruence with values from these different spheres. The paper discusses how institutes try to establish legitimacy in the science–non-science dimension and the public–private dimension and that these attempts sometimes come into conflict with one another. The framework of the legitimacy of hybrid organizations could constitute a fruitful starting point for a discussion of the future place of research institutes in society.