Intrinsic, extrinsic (transition metals and hydroxyl), and induced (color centers) absorption of multicomponent silicate glasses in UV, visible and near IR spectral regions are described. Parasitic effects influencing absorption measurements are discussed. Excitation to the intrinsic absorption band results in intrinsic luminescence and ionization followed by color center generation and phosphorescence. The thresholds of electron and hole mobility in glass network are found in the far UV region. The hole-centers generation as a criterion of substance ionization is proposed. A number of nonlinear mechanisms of glass ionization are discussed. Two-photon ionization was detected in alkaline-silicate glasses exposed to high-power laser radiation in nano- and picosecond regimes. Three- photon ionization was detected in lead-silicate glasses. No reliable data on multiphoton ionization (with number of photons more than 3) of glasses are found. Two- and three- photon cooperative self-multiplication of color centers was found in CuCl-doped glasses. Glass matrix ionization by spectral broadening of femtosecond IR pulses is described. Thermal and surface ionization of glass under intense irradiation by pulsed lasers is described.