The physics of the interaction of high intensity light with matter is presented. New phenomena arising from this are discussed: Starkov shift of atomic levels, multiphoton processes, light-induced refraction, self-focusing of light, etc. It is shown that the basic laws of classical optics - Euclid's law on the rectilinear propagation of light, the law of independence of light beams, Einstein's law for the photoelectric effect, Stokes's rule, etc. - are valid only with low light intensity.