Performance limitations in digital acoustic telemetry are addressed. Increases in computational capabilities have led to a number of complex but practical solutions aimed at increasing the reliability of acoustic data links. These solutions range from ocean-basin scale data telemetry to video-image transmission at a few hundred yards' distance. The opportunity to implement highly complex tasks in real time on modest hardware is a common factor. The data rates range from 1 to 500 kb/s and are much slower than satellite channels, while acceptable system complexity is higher than virtually any other channel with comparable data throughput. The basic performance bounds are the channel phase stability, available bandwidth, and the channel impulse response fluctuation rate. Phase stability is of particular concern for long-range telemetry, channel fluctuation characteristics drive equalizer, and synchronizer design; the bandwidth limitation is a direct constraint on data rate for a given signaling method. >