Single-molecule Raman scattering: including single-molecule nonlinear optics in single-molecule tip-enhanced Raman scattering (TERS), the application of single-molecule TERS in (1) understanding the mechanism of chemical reactions and photo-chemistry as well as catalytic processes on surfaces, and (2) nanoscale chemical mapping of bio-molecules on surfaces, particularly labeling-free real-space sequencing of DNA/RNA and protein molecules. Exploration of single-molecule Raman photons as a potential single photon source and its application in quantum information processing will also be carried out in the near future.