The book presents the Proceedings of the course of the same name, organized by the International School of Atomic and Molecular Spectroscopy of the Ettore Majorana Centre for Scientific Culture, and held in Erice, Italy, from 15 to 30 June 1997. Topics covered include the study of ultrafast phenomena, such as nonequilibrium phonon effects, evolution of excitations at surfaces, dynamics of electrons in semiconductors and metals, rapid conformational changes in molecules and optical control of the quantum states of molecules and solids.