When inhomogeneous broadening is eliminated, the no-phonon lines in spectra (absorption, luminescence, hot luminescence, light scattering, excitation of luminescence, hole burning) actually become the optical analogs of the Mössbauer γ-resonance lines of very high resolution and sensitivity. Photochemical hole burning is an effective method to eliminate the inhomogeneous broadening and to perform high resolution frequency-selective photochemistry. Photochemical hole burning by cw-lasers provides high resolution spectroscopy of molecules and new possibilities of high capacity data storage; by picosecond pulses - storage of their temporal structure, time-and-space domain holography, photochemically accumulated photon echo phenomena.