Laser-based optical spectroscopies are powerful and versatile techniques that are continuing to evolve and find new applications. This book presents reviews of recent progress in our understanding of the spectra and dynamical processes of optically excited states of condensed matter, focusing on the advances made possible by the application of laser-based optical spectroscopies. Reviews are given of the optical properties of crystalline and amorphous semiconducting materials and structures, the properties of defect centers in insulators, two-photon nonlinear processes in insulators, optical...