Pulsating and eccentric binary stars play a fundamentally important role in deciphering the mass distribution within stars. The present volume reviews the fundamental concepts of both radial and nonradial oscillations in the stars including the Sun. Helio- and astroseismological results are reviewed from the basics to the most recent developments. A new theory is presented which seems to explain the mechanism of the light and radial velocity variations of recently discovered Ap stars. This textbook covers almost all kinds of variable stars of widely different characteristics. It will serve as a reference text for a very long time to come not only for specialists but also for undergraduate students of physics and astronomy.