This introduction to the use of radar for remote sensing of natural surfaces provides the reader with a thorough grounding in practical applications, focusing particularly on terrestrial studies that may be extended to other planets. An historical overview of the subject is followed by an introduction to the nomenclature and methodology pertaining to radar data collection, image interpretation and surface roughness analysis. The author presents a summary (illustrated with examples from the natural environment) of theoretical explanations for the backscatter properties of continuous rough surfaces, collections of discrete objects, and layered terrain.