This book summarizes the latest advances in helioseismology, including the measurement of the internal stratification of the sun, the assessment of thesensitivity of oscillations to uncertainties in fundamental physics, and thestudy of the angular velocity and the dynamics of the convection zone. Of particular interest is the structure of the solar core and its relevance to the neutrino problem. The understanding so gained permits one to look ahead confidently to problems concerning the evolution of sun-like starsthat might be addressed by seismological techniques.