Modern coating techniques offer the possibility of corresponding to the increased requirements on component surfaces by the application of thin, high property functional coatings. Thermal sprayed coatings are produced in air (APS), vacuum (VPS) and inert atmospheres (IPS). Underwater plasma spraying (UPS) is an addition to these process variants which completely operates under water. Up to now a lot of different materials including carbides, oxides and other materials such as MCrAlY, cermets and nickel based hard alloys have been processed under water. Dense coatings with thicknesses up to 0,2 mm/layer have been achieved. An autoclave allows spraying at increased pressure levels simulating greater water depths up to 30 m. This publication reveals the technology of underwater plasma spraying used for the production of coatings and powder treatment.