Helio- and asteroseismology are fast- developing new fields of research that probe the internal structure of stars. The complicated multi-periodic oscillations are studied from both theoretical and observational points of view. Nine articles review the state of the art, including modeling the sun, excitations of oscillations, inverse problems, and the observations of seismic phenomena. One section is devoted to the seismology of stars, a field of research still in its very early development. In addition the reader will find about forty research papers on these subjects.