Air-sea interaction is concerned with the coupling between the atmosphere and ocean. This coupling is a highly nonlinear turbulent process with a great deal of feedback. It is fundamental to the motions of both fluids. The winds produce waves and currents. Thus the ocean (and the land too, of course) brakes the atmospheric motion by extracting momentum and mechanical energy. The ocean in turn gives off heat, both sensible and latent (in the form of water vapor); this heat provides one of the main energy sources for atmospheric motions. The nature of this energy source is affected by the turbulence produced by the frictional (braking) effects, and the spatial distribution is affected by the currents. This coupling involves a very broad range of scales from milliseconds to centuries in time ind from microns up to the earth's circumference in space.