Resonance Stark effects are nonclassical Stark effects associated with excited-state charge-transfer processes. The theory of resonance Stark effects developed in Part 2 of this series is generalized in a number of respects. The equations are modified to allow for violations of the Condon approximation and to allow for inhomogeneous contributions to absorption and Stark line shapes. A distinction is drawn between higher-order Stark spectra and Stark spectra that depend on integral powers of the applied electric field, and it is shown how this can affect analyses of resonance Stark effects. Covariances among the parameters that are used to fit absorption spectra and resonance Stark effects are described, and their impact is described in the context of the data for photosynthetic reaction centers that is presented and analyzed further in Part 4 (Treynor, T. P.; Yoshina-Ishii, C.; Boxer, S. G. J. Phys. Chem. B, 2004, 108, 13523. Equations are derived that provide a mapping between the parameters used in Marcus theory and those used in radiationless transition theory.