The interaction of light with an object, such as a microscope specimen, results in the generation of both near-field and far-field light components. The far-field light propagates through space in an unconfined manner and is the "normal" light utilized in conventional microscopy. The near-field (or evanescent) light consists of a nonpropagating field that exists near the surface of an object at distances less than a single wavelength of light. Light in the near-field carries more high-frequency information and has its greatest amplitude in the region within the first few tens of nanometers of the specimen surface. Because the near-field light decays exponentially within a distance less than the wavelength of the light, it usually goes undetected. In effect, as the light propagates away from the surface into the far-field region, the highest-frequency spatial information is filtered out, and the well known diffraction-based Abbe limit on resolution is imposed. By detecting and utilizing the near-field light before it undergoes diffraction, the near-field scanning optical microscopy (NSOM) makes available the full gamut of far-field optical contrast-enhancing mechanisms at much higher spatial resolution. In addition to non-diffraction-limited high-resolution optical imaging, near-field optical techniques can be applied to chemical and structural characterization through spectroscopic analysis at resolutions beneath 100 nanometers.