A review is given of detection and estimation methods in current use in radio and radar astronomy. Methods of determining position and brightness distribution of radio sources by narrow-beam antennas, interferometry or lunar occultations are discussed. Observational procedures for the estimation of frequency spectra are explained. The fundamental problem in radar astronomy, viz., that of mapping, is reviewed, and several methods for the removal of ambiguities are considered. Schemes for the determination of range and velocity of a planet are also described.