The term fishes is used broadly to include the eel-like, cartilaginous jawless fishes (Agnatha), the cartilaginous jawed fishes (Chondrichthyes), and the bony fishes (Osteichthyes). Among these groups, most bioacoustics research has focused on bony fishes, which generate communication sounds via the swim bladder and/or skeletal components. Fishes that have been studied in detail generally hear frequencies below 3000 Hz. The main functions of sounds emitted by fish are for intraspecific or interspecific aggression, defense of a territory or nest, attraction of a mate, and courtship. Although sound production and reception by fish are most often quantified in the frequency domain, behavioral studies indicate that information is conveyed primarily via temporal and amplitude cues rather than frequency. Relatively little is known about hearing in chondrichthyans (commonly referred to as cartilaginous fishes) and the agnathans (commonly referred to as jawless fishes), and no communication sounds have been reported for these groups. For species that do not produce sounds, the auditory system may serve mainly as a type of scene analysis, identifying the abiotic and biotic components of the environment that produce distinctive sounds (e.g., breaking waves, predators, and prey). This chapter reviews studies of the production, detection, and use of sounds by fishes with specific examples from the best studied species. The sources of human-generated (anthropogenic) noise that could potentially negatively affect the capacity of fishes to sense acoustic signals that are required for the long-term survival of a species are also evaluated based primarily on field studies.