According to Orban and Glickman et al. (1968) trauma from occlusion (TFO) is defined as, when occlusal forces exceed the adaptive capacity of the periodontal tissues, the tissue injury results. This resultant injury is termed as \"trauma from occlusion\". World Health Organization, in 1978, defined trauma from occlusion as \"Damage in the periodontium caused by stress on the teeth produced directly or indirectly by the teeth of the opposing jaw.\" Role of the trauma from occlusion in the progression of periodontal disease, pathologic tooth migration, and physiological adaptive capacity of the periodontium to occlusal forces are discussed in this chapter. Various types of occlusal forces include normal or physiological occlusal forces, continuous forces, impact forces, and jiggling forces, which are briefly explained.