  The main obstacle in exploiting the frequency data of $\delta$ Sct stars is
difficulty in mode identification. The $\delta$ Sct oscillation spectra, unlike
those of the Sun or white dwarfs, do not exhibit very regular patterns. Thus,
the mode identification must rely on sophisticated methods, which involve
combined multi-passband photometry and radial velocity data, with an
unavoidable theoretical input from stellar atmosphere models. Moreover, there
are serious uncertainties in theory of $\delta$ Sct stars that have to be
solved. Mode identification and determination of global and internal structure
parameters for $\delta$ Sct stars has to be done simultaneously. I describe in
some detail the methodology and present some recent results we obtained
concerning degrees of excited modes, global stellar parameters, and constraints
on models of subphotospheric convection, as well as effect of rotational mode
coupling.
