This book will describe from fundamental, first principles modern methods of optical spectroscopy. In particular, detailed descriptions of spectroscopic techniques will be developed and organized within the framework of the Perturbative Polarization Expansion approach. This unifying viewpoint allows linear and nonlinear, resonant and nonresonant, spontaneous and stimulated, frequency and time domain spectroscopies to be developed in a semi-classical framework from first principles, i.e. from Schrodinger and Maxwell equations starting points. In particular, descriptions of absorption (electronic and vibrational), Raman scattering and Raman based interactions, CD, near-field effects and nonlinear spectroscopies such as second harmonic generation, sum frequency generation, pump-probe, CARS, photon echoes will be developed and the relationship between these various optical techniques will be highlighted. Nonperturbative and purely quantum matter radiation interactions will also be explicitly considered. Applications to both molecular, condensed phase and materials systems will be cited as examples.This book will describe from fundamental, first principles modern methods of optical spectroscopy. In particular, detailed descriptions of spectroscopic techniques will be developed and organized within the framework of the Perturbative Polarization Expansion approach. This unifying viewpoint allows linear and nonlinear, resonant and nonresonant, spontaneous and stimulated, frequency and time domain spectroscopies to be developed in a semi-classical framework from first principles, i.e. from Schrodinger and Maxwell equations starting points. In particular, descriptions of absorption (electronic and vibrational), Raman scattering and Raman based interactions, CD, near-field effects and nonlinear spectroscopies such as second harmonic generation, sum frequency generation, pump-probe, CARS, photon echoes will be developed and the relationship between these various optical techniques will be highlighted. Nonperturbative and purely quantum matter radiation interactions will also be explicitly considered. Applications to both molecular, condensed phase and materials systems will be cited as examples.This book will describe from fundamental, first principles modern methods of optical spectroscopy. In particular, detailed descriptions of spectroscopic techniques will be developed and organized within the framework of the Perturbative Polarization Expansion approach. This unifying viewpoint allows linear and nonlinear, resonant and nonresonant, spontaneous and stimulated, frequency and time domain spectroscopies to be developed in a semi-classical framework from first principles, i.e. from Schrodinger and Maxwell equations starting points. In particular, descriptions of absorption (electronic and vibrational), Raman scattering and Raman based interactions, CD, near-field effects and nonlinear spectroscopies such as second harmonic generation, sum frequency generation, pump-probe, CARS, photon echoes will be developed and the relationship between these various optical techniques will be highlighted. Nonperturbative and purely quantum matter radiation interactions will also be explicitly considered. Applications to both molecular, condensed phase and materials systems will be cited as examples.