The principle of synthetic aperture radar (SAR) image formation is reviewed in preparation for a discussion of both optical and digital processing techniques. The tilted-plane optical processing approach is presented as being representative of optical techniques. Since the newer digital approaches can take several forms, three classes of digital processors are examined: direct convolution, frequency multiplexing, and frequency analysis of dechirped data. A subjective listing of the relative merits for both processing media is presented. Both are found to be technically viable. The final choice will depend primarily upon the application requirements.