These 20 years have seen much progress in understanding of underwater sound propagation. Few new topics have appeared, but far more complex problems can now be handled—in considerable part, thanks to computers. Emphasis has shifted to lower frequencies, longer ranges, and wave‐theoretical methods. We are still limited by extreme variability of the medium and its boundaries, and by a gap of understanding between mechanical—chemical and acoustical properties. Efforts to narrow this gap should continue, as should the search for “invariants” of problems and for statistical theories to match averaged data.