Spectrum variability of CP stars (Review)

The significant steps which have contributed to our current understanding of the peculiarity of A- and B-type stars phenomenon are reviewed. This presentation is framed in terms of the rotational variability of the spectra of A- and B-type stars. Continuing attempts to detect the light and spectrum variability, and the occurrence of magnetic field in Am and HgMn-stars are both addressed. CP stars as radio and X-ray emitters are also mentioned.