The ocean surface is a complex boundary where air-sea fluxes of mass, momentum and energy take place. The processes in this dynamic interface are of crucial importance for ocean circulation and ecosystems in general. The coupling between surface gravity waves, winds and currents in the adjacent turbulent boundary layers influence the weather and are important for the structural behavior and fatigue of off-shore wind turbines in particular. The dependence of sea-surface drag on environmental conditions and the characteristics of upper ocean turbulence in windy conditions still remain unresolved. There is huge gaps in our knowledge about air-sea interaction. Direct measurements are needed in the upper ocean in order to improve the understanding of the surface boundary layer of the ocean and its representation in numerical models in the form of validated parametrizations.