Responsible for large exchanges between the Ocean and the Lithosphere, oceanic hydrothermalism covers wide scientific domains, from the ocean chemistry to metallogeny. The exploration covers all scales, from the hydrothermal site to the Mid-oceanic ridge system. Modern bathymetry and imagery are required. Physical and chemical anomalies created in the ocean are used to detect and map its distribution. A specific effort in the field of ROV (Remote Operated Vehicle) is needed to acquire data at the corresponding working scale.