Narrow profiles of purely electronic zero-phonon lines open up attractive possibilities for spectral investigation with the use of the Doppler effect (Doppler spectroscopy). It is established that, for a 10-MHz-wide zero-phonon line to shift to a new position, the velocity of motion of a receiver with respect to a source needs to be only ∼10 m/s. It is shown that the narrower the line or the spectral hole (its negative image), the more efficient the Doppler spectroscopy. The possibility of measuring the shape of spectral holes with the use of Doppler spectroscopy is demonstrated, and the potentialities of supersensitive Doppler spectroscopy are considered. The specific feature revealed in the frequency modulation by Doppler spectroscopy is that it occurs without a perturbation of the internal states of the emitter and absorber. The conclusion is drawn that there is a need to study the interference of a photon with itself when the frequency of “one-half of it” changes with the use of Doppler spectroscopy.