The history, current state, and future potential of acoustics in fisheries research and management will be addressed. Fisheries management worldwide is undergoing a fundamental paradigm change in response to population pressures and overharvesting of marine and freshwater stocks. Future fisheries management will be more conservation based and responsive to ecosystem considerations. These trends will demand more comprehensive knowledge of the components of fisheries’ ecosystems and their dynamics, and more realistic estimates of the precision of ocean measurements. Acoustics is poised to take a new and leading role in these developments. Acoustics is nondestructive of marine life, can be near-synoptic, and can measure most of the water column. However, acoustic methods are still hampered by problems with detectability, especially near boundaries, uncertainties about target strengths of the myriad of species and life stages whose scattering properties are complex and behaviorally mediated, and taxonomic identification. These problems will be discussed, and a general experimental plan will be laid out to solve them. The 21st century of fisheries belongs to acoustics and allied technologies.