Surface-enhanced Raman scattering combines extremely high sensitivity, due to enhanced Raman cross-sections comparable or even better than fluorescence, with the observation of vibrational spectra of adsorbed species, providing one of the most incisive analytical methods for chemical and biochemical detection and analysis. SERS spectra are observed from a molecule-nanostructure enhancing system. This symbiosis molecule-nanostructure is a fertile ground for theoretical developments and a realm of applications from single molecule detection to biomedical diagnostic and techniques for nanostructure characterization.