Since 1975, and the identification of the solar 5-minute oscillations as global acoustic modes, helioseismology has proven to be a very active field. It enabled thorough investigation of the physical processes occurring inside the stars, thanks to the extreme precision of the measured frequencies. In 1995, a new step was achieved with the completion of the GONG network and the launch of the SoHO satellite, increasing by several order of magnitude the quality of the available data. The IAU 181 Symposium was chosen by all these consortia as a key time to present their first results. This book contains a synthesis of the progress in the observations and of up-to-date knowledge of the internal structure and rotation of the Sun inferred from helioseismology. It also presents our expectation of what can be learned about other stars with asteroseismology.
