THE USE OF ELECTROMAGNECTIC RADIATION (EMR) for the analy sis of paints and coatings is best addressed by looking at the way this energy source is absorbed by the system under investigation. Most EMR analytical techniques attempt to measure the energy difference between the incident beam and the emerging beam and to relate this energy difference at a particular wavelength (energy) to the absorbing species' concentration or chemical makeup. The emerging beam may pass through the system or be reflected from a surface. There are many sophisticated instruments that use EMR, and they operate from the lowest energy bands in microwaves to the highest energy γ-rays. The region of the spectrum most commonly used in the paint laboratory lies between the infrared and ultraviolet bands. The instrumentation operative in this region can be relatively low in price, and the information that can be obtained about concentration and molecular structure is very useful.