In the framework of Digital Signal Processing, the Parametric Modeling of Signals offers as a natural byproduct a class of Spectral tools, namely the so-called Rational Spectra. This class of Spectra (and their associated Estimators) applies to the case of Stationary as well as Non-Stationary Signals and Random Processes. This important text brings together the significant advances that have been achieved over the last ten years from the confrontation of the theory and its variety of applications.