This book presents the latest developments and issues in both experimental and theoretical studies of multi-photon processes and the spectroscopy of atoms, molecules and nanomaterials in Physics, Chemistry, Biology and Material Science. It is an important addition to an advanced series that contains review papers suitable for both active researchers in these areas and non-experts who wish to enter the field. Special attention is paid to the recent progress of nonlinear photon-matter interactions applied to femtosecond laser induced nonadiabatic molecular alignment, high-order harmonic generation from C60 fullerene plasma, resonant femtosecond stimulated Raman spectroscopy and attosecond pulse generation, as well as near-field optical imaging of noble-metal nanoparticles and photoexcited ultrafast electron transfer in condensed phase.