This lecture will review laboratory and field data on the distribution of bubble sizes due to rain and breaking waves and compare them with theoretical distributions where appropriate. Present gaps in our knowledge will be indicated. The applications to underwater acoustics are of two kinds: active generation of sound by bubble formation, and passive backscatter or absorption of incident sound waves. Each of these depends to some extent on the horizontal and vertical variations in bubble density. Inversely, one can obtain information on rainfall, breaking waves, and near-surface currents.