Optical spectroscopic methods are widely used in the study of optical and other properties of di erent materials. e various techniques are usually based on measuring absorption, emission, or scattering of light that contains information about physical properties of the materials. Commonly used techniques include electronic absorption (UV-vis), photoluminescence (PL), infrared (IR) absorption, and Raman scattering. O ther mo re s pecialized te chniques i nclude uorescence c orrelation s pectroscopy (FC S), dynamic light scattering (DLS), uorescence lifetime imaging microscopy (FLIM), total internal re ection uorescence (TIRF), surface-enhanced Raman scattering (SERS), and single-molecular spectroscopy (SMS). ese various techniques can provide di erent information about the molecular properties of interest. In this chapter, several common spectroscopic techniques are reviewed with emphasis on their principles of operation as well as spectral interpretation. e main objective is to explain how one can obtain useful physical information about the materials under study from the optical spectra measured experimentally.