Paul Smeyers is professor em. in astrophysics at the Institute of Astronomy of the Catholic University Leuven, Belgium. Tim Van Hoolst is part-time professor at the same institute and senior research scientist at the Royal Observatory of Belgium. Both are long-time teachers and researcers in the field of stellar oscillations.

Basic Concepts.- The Equations Governing Linear Perturbations in a Quasi-Static Star.- Deviations from the Hydrostatic and Thermal Equilibrium in a Quasi-Static Star.- Eigenvalue Problem of the Linear, Isentropic Normal Modes in a Quasi-Static Star.- Spheroidal and Toroidal Normal Modes.- Determination of Spheroidal Normal Modes: Mathematical Aspects.- The Eulerian Perturbation of the Gravitational Potential.- The Variational Principle of Hamilton.- Radial Propagation of Waves.- Classification of the Spheroidal Normal Modes.- Classification of the Spheroidal Normal Modes (continued).- Completeness of the Linear, Isentropic Normal Modes.- N 2(r) Nowhere Negative as Condition for Non-Radial Modes with Real Eigenfrequencies.- Asymptotic Representation of Low-Degree, Higher-Order p-Modes.- Asymptotic Representation of Low-Degree and Intermediate-Degree p-Modes.- Asymptotic Representation of Low-Degree, Higher-Order g +-Modes in Stars Containing a Convective Core.- Asymptotic Representationof Low-Degree, Higher-Order g +-Modes in Stars Consisting of a Radiative Core and a Convective Envelope.- High-Degree, Low-Order Modes.- Period Changes in a Rapidly Evolving Pulsating Star.