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.
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