In 1960, the solar surface was found to be moving radially with a period of 5 min. The cause of this effect was found to be the trapping of acoustic waves in the solar internal thermal gradient. Since the sound fills a resonant cavity, only specific oscillatory modes are present whose characteristics depend on the plasma properties. Thus, the solar interior can be remotely sensed by observing the trapping region’s upper boundary at the surface. This led to the field of helioseismology and produced new information about the solar internal rotation rate, composition, neutrino flux, convection zone depth, and internal changes associated with the solar activity cycle. It has also generated progress in remote sensing techniques (acoustic holography, ring diagrams, inversions), observing facilities (GONG Network, MDI instrument on SOHO), and insights into the coupling of turbulent convection and sound. Presumably, other stars also contain sound and their interiors could thus be probed, but so far no conclusive observations of these vibrations have been obtained. [Work supported by NSF and NASA.]