Acoustical oceanography involves the use of inverse acoustic techniques to investigate physical and biological phenomena in the sea. Processes at the sea surface, including bubble formation from wave breaking, precipitation rates, and gas transfer across the air--sea interface, are all being interrogated using active and passive acoustic techniques. Novel methods for monitoring fish stocks, based on the acoustic properties of the swim bladder, are also receiving attention. The acoustic calls of marine mammals are being investigated as natural sound sources to characterize the ocean environment. New geo-acoustic models to marine sediments have been developed and incorporated into ambient noise inversion techniques for determining seabed properties. Time-reversal experiments have been conducted over ranges of several kilometers, successfully stabilizing acoustic arrivals and allowing fluctuations in the ocean to be characterized. Brief accounts of these topics will be presented.