The Royal Belgian Institute of Natural Sciences (RBINS) has an extensive and well established collaboration with volunteers in almost all its directorates (Taxonomy & Phylogeny, Public Services, Natural Environment, Scientific Heritage Service, Earth and History of Life). The nature of the activities of the «Citizen Scientists» (CSts) is really varied. With their help, the RBINS complements the lack of expertise in some research fields. They also valorize the scientific collections by studying them, as a result improving collection management of the collections and their accessibility. The goal of the « Citizen Science Day » was two fold: 1) highlight the work of the volunteers during a day of meeting and sharing experiences and 2) To show the diversity of projects, types of collaborations and areas of research that they contribute to within the Institute. They were invited to attend presentations and to exchange on their practices, expectations and wishes during a lunch, a movie and finally a cocktail.