Side‐scan sonar is the equivalent of synthetic‐aperture radar, a University of Michigan development in the 1950's. Then classified, it was first described in the open literature in 1966 in communication theory terms. The similarity of the synthetic aperture technique to holography was pointed out by the author in 1967, and a 1968 paper co‐authored by laser holography pioneer Emmett Leith (a co‐author of the 1966 synthetic aperture paper) noted that “the holographic viewpoint has led to designs which are not easily explicable from the communication theory viewpoint.” Because radar and sonar are both echo‐location systems, papers on the use of synthetic aperture concepts in sonar began appearing in 1968, including a 1974 paper describing synthetic‐apertureB‐scan sonar techniques in medical applications, and a 1970 U.S. patent on synthetic‐aperture ultrasonic imaging techniques. The present paper reviews the side‐scan principles, its recent advances and applications and briefly describes the possibilities of holographic space‐frequency equivalence [W. E. Kock, International Optical Computing Conference (I.O.C.C. 78), London, England, September 6, 1978] in side‐scan sonar. [Work supported by the Herman Schneider Laboratory.]