Apart from publishing Recommendation on the Status of Scientific Researchers and the subsequent Recommendation on Science and Scientific Research (1974 and 2017, respectively), UNESCO has been a significant agent in international science cooperation since 1945. The ‘S’cience in UNESCO was, however, a last-minute addition, which was closely tied to the beginning of the nuclear age, and the creation of the previously unthinkable, annihilative power of the nuclear bomb. The science department of UNESCO was thus created at a time when science did not only promise endless, modern progress to the broader public as well as to many politicians, but also threatened world destruction. In the following decades, the onset of the Cold War posed its own challenges to the idealized norms of science as proposed by Robert K. Merton in 1942 (universalism, communality, disinterestedness, and organized skepticism), as well as to the ideas of international science cooperation in general. In this chapter, Christensen traces the different ideas of science as they were articulated within UNESCO, thereby illustrating what the organization itself understood by the concept of science and its relations to concepts of modernity, progress, and development.