The Archive of the Université Libre de Bruxelles currently holds approximatively 4,000 slides, mostly inherited from the former “Cité scientifique”, an early public-privatepartnership, bringing together the ULB (professor Paul Héger), the industry (director Ernest Solvay) and the city of Brussels (mayor Charles Buls). When its institutes were closed and their heritage had to be moved, the slides sets were dispersed and ended up at several different departments of the university. The slides of the different collections produced in the laboratories are directed by Paul Héger (biology), Léo Errera (biology), Jean Massart (biology), Émile Waxweiler (sociology, biology) and probably others. The topics in the collection represent the history of science, (micro-)biology, zoology, medicine, colonial history etc.