This article reviews the new developments in Tip-enhanced Raman scattering; (TERS). The fundamental mechanisms underlying the Raman enhancement are; discussed, including the role of the plasmonic character of the metallic tips,; the nature of the optical tip-sample coupling and the resulting local-field; confinement responsible for ultrahigh spatial resolution down to just several; nanometers. Criteria for the distinction of near-field signature from far-field; imaging artifacts are addressed and TERS results of molecules and; nanostructures are presented. With enhancement factors as high as 10$^9$,; single molecule spectroscopy is demonstrated. Spatially resolved vibrational; mapping of crystalline nanostructures and determination of crystallographic; orientation and domains is shown making use of the unique symmetry properties; of the tip in conjunction with the intrinsic Raman selection rules.
