  The results obtained by means of the photometric approach to the study of
Delta Sct stars are extensively discussed. The different frequency contents of
the three best candidates for asteroseismological studies (FG Vir, 4 CVn and XX
Pyx) are presented and compared; the importance of the amplitude variations and
of the combination terms is emphasized. The analysis of other multiperiodic
variables shows how a large variety of nonradial modes are excited; in some
cases, modifications of the power spectrum can be observed over a few years and
new modes can be seen to grow. Among monoperiodic pulsators, constant as well
as variable amplitudes can be observed. The difficulty of identifying an
oscillation yielding quantum numbers is emphasized; the possibilities offered
by $\delta$ Sct stars belonging to binary systems and open clusters are
discussed. In this respect, combining the photometric and the spectroscopic
approaches could lead to a solution. A comparison is also made between low- and
high-amplitude pulsators, finding similarities. The use of a reliable
Period-Luminosity-Colour relationships toward the shortest periods can greatly
help mode identification in the galactic stars; moreover, it could provide an
independent verification of extragalactic distances.

Astrophysics