Using the example of a problematic airborne contaminant found on a component worked on in a clean room, the article outlines the methods employed to identify small particles using the light microscope (LM). Morphological analysis starts with a low power examination. Microscopy with polarized light (PLM) and a first order red filter then provides additional characteristics (including birefringence, extinction, isotropy, polarization colors and refractive index). Dispersion staining can help identify colorless, transparent particles. Basic microscopical methodology is outlined for identification of unknown clean room contaminants, 95% of which are usually quartz sand, limestone, or cotton. The four main categories are fibers, minerals, biological substances and industrial particulates. Thirty-one photomicrographs (70x magnification) illustrate common particles and the individual characteristics which identify them m included are: viscose rayon, hardwood pulp, cement, carborundum, quartz, talc, limestone, bituminous coal, pine pollen, ragweed pollen, potato starch, cotton, orlon, chemical coniferous wood, asbestos, mica, tourmaline, prehnite, steatite, nylon, cellulose acetate, polythene (polyethylene), phenolic resin, zircon, metal shot, metal shavings, pulverized coal fly ash, leaf burnings, oil soot, and incinerator fly ash.