In an ideal infrared optical system, all available energy in the wavelength region of interest would be transmitted to the detector. But, every surface in an optical system distributes incident energy into reflected, transmitted and absorbed portions. The usefulness of interference coatings is based on their potential for altering the properties of surfaces to provide optimum use of available energy. Interference coatings are discussed here with respect to their influence on energy distribution at surfaces. The discussion will include coatings for reflecting and transmitting components, as well as filters and beamsplitters. Theoretical data and measured performance are used to show how well available coatings utilize the energy incident on them.