Rapidly oscillating Ap stars constitute a unique class of pulsators to study nonradial oscillations under some – even for stars – unusual physical conditions. These stars are chemically peculiar, they have strong magnetic fields, and they often pulsate in several high-order acoustic modes simultaneously. We discuss here an excitation mechanism for short-period oscillation modes based on the classical κ mechanism. We particularly stress the conditions that must be fulfilled for successful driving. Specifically, we discuss the rôles of the chemical peculiarity and strong magnetic field on the oscillation modes and what separates these pulsators from δ Scuti and Am-type stars.