The vestibular system (VS), and more specifically its otolithic part (specialized in detecting gravity and inertial linear acceleration), has long been recognized for its role in spatial orientation and postural equilibrium. Its involvement in the regulation of other physiological systems (respiratory and cardiovascular systems, circadian regulation, food intake, bone mineralization) has been made clear only recently. Besides an increase in basic scientific knowledge, studying the biological impact of VS is also crucial for space exploration because it could participate in some harmful effects of prolonged exposure to weightlessness - such as cardiovascular and sensory-motor deconditioning, bone loss, and hormonal changes. VS dysfunction could also be implicated in common pathological conditions such as orthostatic hypotension, sleep disruption, bone loss…Studying the biological effects of the otolith system can be performed by removing it or, more physiologically, by changing the level of gravity. Hypergravity can be produced by centrifuges while reduced gravity can only be obtained during parabolic or space flights. There are few ground alternatives, such as head-down bed rest and dry immersion, for studying some aspects of the effect of weightlessness on physiological systems. These facilities are scattered throughout Europe, Russia and the USA and no single scientific team has the expertise in all the main scientific fields relevant to gravitational physiology: neurosciences, musculo-skeletal physiology, endocrinology, chronobiology, and cardiovascular physiology. Thus, ambitious scientific research on the implication of VS in gravitational physiology is not conceivable without international cooperation. The aim of this proposal is to establish long-term research cooperation on VS and gravitational physiology at an international level, involving the main research facilities in Europe, Russia and the USA, and to create new research opportunities in this area.