This chapter details the basics of radar backscattering over a rough surface (such as the sea) as well as the sea surface mapping by a synthetic aperture radar. Nonlinear phenomena involved in the sea SAR mapping, from the intrumental as well as hydrodynamic points of view, are detailled. Finaly, the presentation reminds the usual techniques to invert the SAR image (i.e. retrieve the sea surface spectrum) or to estimate the bathymetry from the current modulation and its effect on the roughness surface.