Outstanding Issues for Post-Main Sequence Evolution:

We review the question of the empirical and theoretical instabilityregions in the HR diagram for evolved, compact stars. These include thethree families of pulsating white dwarfs (g-mode pulsators excitedthrough mechanisms associated with partial ionization and convection inthe stellar envelope), the pulsating subdwarf B stars (p-mode variablesexcited through a classic kappa mechanism associated with the radiativelevitation of iron in the stellar envelope), and the `Betsy stars',the brand new class of long-period, g-mode pulsators of the subdwarf Btype discovered recently.