Laser trapping has been used for the manipulation of a wide variety of microscopic inorganic, metallic, polymeric, and biological particles, including cells, bacteria, and viruses. A more recently developed technique, optical chromatography, uses a lightly focused laser beam introduced into a counter-propagating fluid containing the particles to be trapped. Particle trapping and separation occurs through a balance of fluid drag forces and optical forces. The optical pressure that the laser exerts on a particle depends in part on its size, shape, and refractive index (chemical composition). Particles with a larger refractive index experience greater optical pressure and hence move farther upstream. Particles move against the fluid flow until reaching an equilibrium position where the fluid and optical forces are balanced. This position in relation to the focal point is termed the retention distance. Several important samples of biological origin have been separated and studied, including bacterial cells, spores, and pollens. The utility and prospects for optical chromatography are greatly expanded and the stage is set for many other optical characterization applications.