Some typical resonance nonlinear-optics phenomena taking place when light interacts with atoms are considered. The multitude of such phenomena reduces to scattering of the perturbing light, perturbation of the atomic spectrum, excitation of an atom and its ionization. In all these cases the investigations are carried out using the simplest model--an isolated atom in a monochromatic external field. Such a model enables one to give an exact description of many elementary processes. On the other hand it is sufficiently realistic. A detailed investigation is carried out of resonance fluorescence, spontaneous Raman scattering, multiphoton excitation of atoms, resonance shifts and splitting of atomic levels and resonance lonication of atoms. The nature of these processes is investigated as a function of the intensity of the external field, its frequency, a specific atomic spectrum, the nature of polarization of the perturbing field, and the degree of its nonlinearity. The role played by the field of the electromagnetic vacuum is analyzed. Theoretical predictions are compared with the results of many experiments describing resonance processes of the interaction of an intense light field with atoms.