Current knowledge of the physical effects of underwater explosions on the environment is summarized, with particular attention to the heating of water, the mixing of explosion products with water, and cratering. Theory and data indicate that thermal effects on the environment are negligible because rapid turbulent mixing reduces any temperature excess to a negligible amount within minutes. Virtually no data are available on the mixing of explosion products with water and air. However, information on the bubble and surface phenomena of underwater explosions has been utilized to provide qualitative guidance concerning the distributions immediately after a test. Existing theories of turbulent diffusion can be applied to calculate the subsequent history of the products. Knowledge of the physical effects of bottom explosions on the environment is limited to crater measurements in shallow water and some data on the behavior of explosion bubbles in deep water. Suggested programs to fill gaps in current knowledge are outlined. (Author).