Multiphoton Processes in Atoms in intense laser-light fields is gaining ground as a spectroscopic diagnostic tool. The authors present descriptions of processes occurring in atoms under the action of strong electromagnetic radiation, in particular, the shift, broadening, and mixing of atomic states. The topics include tunneling ionization, above-threshold ionization, ionization of multiply charged ions, resonance-enhanced ionization, super-intense radiation fields, and properties of Rydberg states strongly perturbed by laser radiation.