NearfieldScanning Optical Microscopy (NSOM )is a relatively new technology that defeats the diffraction limit for optical measurements by utilizing the near field portion of electromagnetism to window down to ~ 10 nm spatial resolution. NSOM instrumentation has progressively developed over the past 15 years, to the point where several different basic techniques are available as commercial instruments The principles of NSOM are very much in play within the research community. NSOM has many different applications ranging from biological studies to nanofabrication. This tutorial provides a basic introduction to NSOM.