The Facial Action Coding System (FACS) is a system to taxonomize human facial movements by their appearance on the face, based on a system originally developed by a Swedish anatomist named Carl-Herman Hjortsjö.[1] It was later adopted by Paul Ekman and Wallace V. Friesen, and published in 1978.[2] Ekman, Friesen, and Joseph C. Hager published a significant update to FACS in 2002.[3] Movements of individual facial muscles are encoded by the FACS from slight different instant changes in facial appearance. It has proven useful to psychologists and to animators.