ABSTRACT. – Sleep is a ubiquitous phenomenon, found in animals of many different phyla. While in the past sleep has been defined through studies on mammals and birds, it has recently appeared that invertebrates might show this behavioural state. The present behavioral study on sleep in Octopus vulgaris demonstrates its presence in a cognitively advanced invertebrate. We studied resting states in sixteen adult Octopus vulgaris to determine the presence of behavioural sleep. Animals were filmed day and night in isolation and before and after they were restdeprived mechanically. Activity cycles were under circadian control and quiescent animals showed an elevated arousal threshold, which was determined by exposing them to growing levels of vibratory stimulation, and state reversibility with intense stimulation. Behavioral observationsalso demonstrated that octopuses chose a preferred resting place, actively built a den site and assumed a typical posture. The quiescence of the subjects often coincided with random movements of the suckers on the arms. Octopuses also showed a typical ‘half-and-half’ skin pattern during the periods of rest, which was not camouflage matched to the environment. Rest deprivation during nighttime led to a rest rebound, while daytime rest deprivation reduced quiescent time. All these findings lead us to the conclusion that, although brain physiological changes might not be parallel, Octopus vulgaris shows typical behavioral sleep.