Progress on Rotational Modulation Studies of Continuum and Line Fluxes

The methodology commonly adopted in studying quasi-periodic flux variations, which are produced by surface inhomogeneities on a rotating star - the so-called rotational modulation study - is briefly reviewed with particular emphasis on recent results concerning the physical characteristics and topology of stellar active areas at various atmospheric levels, such as photospheric spots, chromospheric and transition-region plages and coronal features. The present observational limits are discussed and the need of highly accurate and dedicated photometry is stressed as a necessary and, maybe, sufficient condition for a break-through in the study of stellar activity.