Temporomandibular joint (TMJ) is a complex, sensitive and highly mobile joint. TMJ is the most used joint of the body. Temporomandibular disorders (TMD) are a class of degenerative musculoskeletal conditions associated with morphologic and functional deformities that affect up to 25% of the population. The most frequent structural (as opposed to muscular) cause of TMD is internal derangement. The most common TMJ disorders are pain dysfunction syndrome, internal derangement, arthritis, and traumas. TMD is seen most commonly in people between the ages of 20 and 40 years, and occurs more often in women than in men .The most frequent complaint is pain and a decrease in the maximal interincisal opening (MIO). This book deals with internal derangement and its management including both surgical and non-surgical.