Cetaceans are species with complex social structures and ecological relationships with their habitat. Longitudinal long-term studies (those carried out for more than a decade) reveal basic aspects of the social structure, behaviour of this group of marine mammals. A fundamental aspect of these studies is the individual recognition with photo-identification techniques. In the CETOC project we studied the abundance, frequency, distribution, habitat use, behaviour, social structure, and population trends of target cetacean species.