Vibrational spectroscopy is one of the most popular and valuable tools for scientists and researchers to obtain physicochemical insight into complex molecular systems. Although standard software of quantum chemistry calculations routinely provides predictions of vibrational spectra, it often lacks dynamic aspects and spectroscopic accuracy enough to compare our experimental data directly and strictly to its computational output. The quantum/classical mixed approach presented in this textbook allows scientists and researchers including undergraduate and graduate students of chemistry and physics to extract microscopic information of structure and dynamics of molecules from their vibrational spectroscopic experimental data without any need to ask theoreticians for help.