Development in the art of transducer design and array configuration has been spurred on mainly by two motivating forces: (1) Extensive research in underwater propagation has established the advantages of increasingly lower frequencies for long‐range detection and localization of targets and noise sources. (2) The advent of new piezoelectric and structural materials and of solid‐state electronic devices has led to substantial improvements in transducer performance with regard to sensitivity, power output, and depth of submersion. Theory has kept abreast with these developments, particularly in handling large arrays with their mutual impedance problems, in pointing to digital multibeamforming techniques, and in revealing the significance of waveform design to detection performance. A few new concepts were born and have won acceptance during this period. These include: the generation of sound by hydroacoustic means, the employment of compliant metal tubes for acoustic focusing and reflection, the exploitation of structural flexing modes for sound radiation, and the use of free‐flooded cavity structures as deep submergence sources. As we continue to adapt our sources and receivers to the ocean's transfer functions, noise patterns, and targets—false and true—there will be an increasing need for fundamental research into the acoustic properties of materials and for field test of experimental acoustic detection systems.