Of all massive pulsating stars, the Cephei stars are probably the most important. Their masses lie between 8 and 16 , and thus fall in the range within which theories predict that the minimum mass for type-II supernovae must lie. These stars are in advanced stages of core hydrogen burning, critically controlled by the structures of chemically inhomogeneous regions surrounding their convective cores. We are fortunate in having two nearby young clusters, NGC 3293 and NGC 6231, which are rich in Cephei stars. Asteroseismological studies of these objects will provide us with excellent tools for testing the unknown aspects of massive-star evolution, as well us helping us to understand the chronology of the star-formation process.
The Cephei stars are very bright, in both the optical and the UV. Central to the questions concerning them is how they evolve to red giants, and in particular what are the properties of the Cepheids into which they evolve. At present the Cepheid period-luminosity relation is calibrated observationally. However, a theoretical calibration that takes into account chemical composition, for example, can potentially be considerably more reliable. It is quite feasible, therefore, that with the help of STARS, Cephei stars will play a direct role in establishing the most accurate distance scale for measuring the Universe.