Developments in space exploration, microelectronics, and other high-tech industries have promoted cleanroom technology and increased the need to identify particles sometimes too small to handle with the polarizing light microscope. Light microscopy has traditionally been the most commonly used technique for small particle identification and many microscopists are very proficient in identifying particles using a polarizing light microscope as the principal investigative tool. The polarizing light microscope, in the hands of a good microscopist, is an extremely efficient instrument for particles down to a few micrometers in size. However, in the size range below 5 pm, an instrumental approach to small particle identification is essential. The development of electron microbeam instruments in the early '60s and 70s introduced a new dimension to small particle identification. In these instruments, particles of 1 urn and smaller can be chemically identified when chemical characterization of particles is combined with cathodoluminesence and a relatively simple optical characterization in the instrument itself.