within the waters of the Pelagos Sanctuary for Mediterranean Marine Mammals, mostly in the Ligurian Sea. The core study area extends over about 25,000 km2, encompassing coastal, slope and pelagic waters between continental Italy and France, and the Island of Corsica. The CSR target species are fin whale (Balaenoptera physalus), sperm whale (Physeter macrocephalus), long-finned pilot whale (Globicephala melas), Risso’s dolphin (Grampus griseus), Cuvier's beaked whale (Ziphius cavirostris), striped dolphin (Stenella coeruleoalba), common bottlenose dolphin (Tursiops truncatus) and short-beaked common dolphin (Delphinus delphis). The project focuses on population dynamics, spatial distribution, habitat preferences, behaviour, bioacoustics, photogrammetry, genetics, as well as on the evaluation of long-term environmental changes and monitoring of anthropogenic pressures. The main aim is to produce scientific knowledge to support the conservation of marine mammals. Studies conducted within the CSR project generated one of the longest time series and one of the largest datasets on Mediterranean cetaceans, allowing to evaluate and detect changes in the species’ presence. The data series on Risso’s dolphins, among the longest and one of the most important of its kind, allowed to highlight a dramatic decline of this species in the study area. This result significantly contributed to having the Risso’s dolphins Mediterranean subpopulation listed as Endangered in the IUCN Red List of Threatened species. Habitat preferences of cetaceans living in the Pelagos Sanctuary have been described, allowing also to make predictions of the presence probability of the different species. This information is critical for the management of the Pelagos Sanctuary as it enables vulnerability assessments of marine areas with respect to the existing human pressures. Furthermore data on the variability of cetaceans’ habitat preferences can be used as a basis for the evaluation of the environmental quality of marine ecosystems, as required by the Marine Strategy Framework Directive. The CSR project has many longstanding and profitable collaborations with national and international organisations and research institutes across the Mediterranean. The analyses and the large photographic catalogues shared among institutes allowed to study both short and long-term movements of cetaceans in the Western Mediterranean. It has been observed that Risso’s dolphins and common bottlenose dolphins can cover hundreds of km; sperm whales, over a thousand km, moving from the Strait of Gibraltar to the Ligurian Sea. Cetaceans’ vocalisations are regularly recorded, generating a large acoustic dataset and allowing studies of the vocal repertoire of sperm whales and other species. Behaviour and overall body size