Multiphoton Spectroscopy of Molecules deals with the fundamental theory, methods, and basic results in multiphoton spectroscopy research made possible by using powerful lasers. This book reviews the progress made in visible and UV multiphoton spectroscopy, including the characteristic properties of multiphoton transitions. Certain theoretical methods such as the time-dependent perturbation, density matrix, Green’s function, and susceptibility methods, can point to multiphoton transitions in a molecular system, beginning from first principles. This text also describes the technique in detecting two- or three-photon absorption by multiphoton ionization of molecules. A type of optical mass spectroscopy combining spectroscopic information derived from multiphoton absorption with mass spectrometric information has provided interesting results. This book also discusses the polarization behavior of two-photon absorption processes of molecules. Monson, Mc Clain, and Nascimento have investigated the polarization dependence of the two-photon absorption cross section of randomly oriented, nonrotating molecules. his text also presents the spectroscopic results of excited states confirmed when the multiphoton techniques is applied, as well as some experimental and theoretical approaches related to multiphoton spectroscopy of molecules. Nuclear scientists and physicists, atomic researchers, molecular physicists, and academicians in the field of quantum mechanics or physical chemistry will greatly appreciate the book.