Removable appliances work by simple tipping movements of crown of the teeth about a fulcrum close to the middle of the tooth. They also allow differential eruption of teeth, for example by using bite planes. The success of these appliances was dependent on excellent patient compliance because of their removable nature. The term "functional appliance" refers to a veriety of removable appliance designed to alter the arrangement of various muscle groups that influence and position of the mandible in order to transmit forces to dentition and the basal bone. Typically these muscular forces are generated by altering the mandibular position sagittally and vertically, resulting in Orthodontic and Orthopedic changes. The functional appliances that can be removed by the patient are known as removable functional appliances. This book explains all the aspects of removable appliances in orthodontics.