The quantum/classical mixed approach has provided the most successful results for the IR and Raman spectra of bulk water. It solved a number of longstanding issues about vibrational spectroscopy of water such as the bimodal feature and Evans window of the Raman spectrum, the temperature and pressure dependence of the vibrational spectra, the effect of the intramolecular and intermolecular vibrational couplings on the band shape, the relationship between the hydrogen-bond strength and the peak frequency, the ultrafast dynamics in the excited state, and so on. This chapter introduces some of these issues in detail.