When a radar illuminates the sea, it receives simultaneously the echoes arising from various patches at the surface. However, an appropriate processing of the received signal makes it possible to distinguish the patches at different distances, on operation which is called range processingRange processing. It is also possible to classify the echoes in terms of their induced Doppler shift, an operation which is called Doppler processingDoppler processing. In this chapter we describe these two fundamental operations, which are common to all types of HFR. We explain how the Doppler spectrum can be estimated from a range-resolved radar time series, using a Fourier transform of the windowed signal. We introduce the concepts of coherent summation over an integration time and incoherent summation over an observation time. We recall some classical artefacts of windowing and sampling in the calculation of Doppler spectra and discuss various factors that are responsible for the broadening of the Bragg peaks as well as the expected accuracy in measuring their position.