  Rapidly oscillating Ap stars consitute 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 kappa mechanism. We particularly
stress the conditions that must be fulfilled for successful driving.
Specifically, we discuss the roles of chemical peculiarity and strong magnetic
field on the oscillation modes and what separates these pulsators from delta
Scuti and Am-type stars.
