Abstract: The last 25 years have brought great developments in sonar systems for use over the whole spectrum of underwater applications. This presentation will review the broad variety of applications of and their demands to sonar systems, including offshore, hydrography, dredging, environmental protection, scientific research and defence and security. Emphasis will be put on single- and multibeam sonar systems with presentations of their development over the past 25 years. Their capabilities and limitations at different stages of the development will by highlighted including frequency, bandwidth, beam patterns, resolution, range and depth capabilities etc. The-state-of-the-art in sonar systems today will briefly be presented.