AbstractNon-coherent X-band (8–12 GHz) and S-band (2–4 GHz) marine radars have been used to aid the navigation of ships and monitor the traffic in coastal areas for decades. These traditional marine radar (MR) applications treat the radar return from the sea surface, or sea clutter, as a noise that must be suppressed. In recent years, there has been a growing interest in X- and S-band MR ocean sensing. Non-coherent MRs have shown to yield accurate surface wave frequency-direction spectra, maps of the sea surface elevation, the near-surface current, and the bathymetry, as well as surface wind information, among other parameters, under a broad range of environmental conditions. Meanwhile, MR technology is undergoing a transition towards a fully coherent and solid state architecture. In MR ocean sensing, coherent on-receive magnetron-based systems are finding broader use. It has been shown to yield accurate significant wave heights and is being used to improve our understanding of grazing incidence radar scattering mechanisms. Lately, digital signal processing is becoming more commonplace in off-the-shelf commercial MRs and significantly broaden the scope and potential of oceanographic applications.