This self-directed learning module discusses the deleterious effects of immobilization on the functional capacity of individual organ systems and on the body as a whole. It is a part of the chapter on physiatric therapeutics for the Self-Directed Medical Knowledge Program Study Guide for practitioners and trainees in physical medicine and rehabilitation. This section stresses that the deconditioning effect of immobility has its own morbidity and should be considered separately from the disease or injury that had led to the restriction of physical activity. The management of the immobilization syndrome is also described.