The current volume is a single topic volume on the vibrational intensities in the infrared and Raman spectra. Vibrational intensities in infrared and Raman spectra are important physical quantities that are directly related to the distribution and fluctuations of electric charges in the molecule. These spectral parameters can be experimentally determined with good accuracy for many molecules. Additionally, infrared and Raman intensities are presently estimated theoretically by advanced analytical derivative ab initio molecular orbital methods. These fundamental molecular quantities are being used in structural, and other studies, on a limited basis.