  Peculiar A stars are so named because they exhibit abundance peculiarities in
their atmospheres. It is believed that these arise as a result of
differentiation of chemical species in large magnetic spots in which convective
mixing is inhibited: there might be just two antipodal spots, whose axis is
inclined to the axis of rotation. Many of the Ap stars that are rotating slowly
also pulsate, with periods substantially shorter than the period of the
fundamental radial mode. The pulsations appear to be nonradial, but
axisymmetric, with their common axis usually aligned with the axis of the
spots. In this lecture I shall first discuss the magnetic suppression of
convection in the spots, and then I shall try to explain the pulsation
phenomenon, reviewing some of the suggestions that have been made to explain
the alignment and the excitation mechanism, and finally raising some issues
that need to be addressed.
