Period Changes and Evolution in Pulsating Variable Stars

We review ways in which observations of the changing periods of pulsating variable stars can be used to detect and directly measure their evolution. We briefly describe the two main techniques of analysis -- (O-C) analysis and wavelet analysis -- and results for pulsating variable star types which are reasonably periodic: type I and II Cepheids, RR Lyrae stars, beta Cephei stars, and Mira stars. We comment briefly on delta Scuti stars and pulsating white dwarfs. For some of these variable star types, observations agree approximately with the predictions of evolutionary models, but there still exist significant areas of disagreement that challenge future models of stellar evolution. There may be a need, for instance, to include processes such as rotation, mass loss, and magnetic fields. There may also be non-evolutionary processes which are contributing to the period changes.