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The evolution of the technique of remote sensing of the sea-surface by dekametric radar is traced from the original observation of the Bragg resonant scattering phenomenon by D. D. Crombie in 1955 to its present applications to the measurement of surface wind-direction and wind-speed, wave-height spectrum, wave-directional spectrum and surface-currents. The central role played by the Doppler spectrum of the radar echoes is illustrated. The generation and spectral properties of wind-driven waves on the sea-surface are discussed including wave-wave interactions and the nature of electromagnetic scattering by first and second-order processes is described. An account is given of the techniques used for UK experiments on ground-wave radar surveying the Celtic Sea from West Wales. Synthetic aperture experiments using a moving vehicle permitted the directional spectrum of the sea-surface to be determined. Sky-wave experiments from a radar in Southern England permitted comparisons with sea-state and surface winds measured in the Rockall Bank area of the North Atlantic by oceanographic vessels and buoys. Finally, work in progress in the US and UK on improved narrow beam and interferometer radars and new methods for inversion of measured Doppler spectra to yield seawave spectra are reviewed.