This is a comprehensive list of functional appliances that are used in the field of orthodontics. The functional appliances can be divided into fixed and removable. The fixed functional appliances have to be bonded to the teeth by an orthodontist. A removable functional appliance does not need to be bonded on the teeth and can be removed by the patient. A removable appliance is usually used by patients who have high degree of compliance with their orthodontic treatment. Fixed appliances are able to produce very accurate movement in the teeth Both fixed and removable functional appliances can be used to correct a malocclusion in three planes: Anterior-Posterior, Vertical and Transverse. In the Anterior-Posterior dimension, appliances such as Class II and Class III are used. Appliances used in transverse dimension are utilized to expand either the maxillary or the mandibular arch. Appliances used in the vertical dimension are used to correct open or deep bite. It is important to note that initially dento-facial Orthopaedics was mainly done in Europe. The United States was introduced to Fixed Orthodontics by Edward Angle. Norman William Kingsley was the first person to show "jumping the bite" by using an anterior bite plate. Hotz then developed the Vorbissplate which was a modification of Kingsley's plate. Wilhelm Roux is credited with being the first person who studied the effects of functional forces on Orthodontics in 1883. His workings were then used by other dentists studying dental orthopaedics. His teachings became known as Roux Hypothesis, which Karl Haupl later expanded upon. The Monobloc was developed by Pierre Robin (surgeon) in 1902 and is considered to be one of the first functional appliances in Orthodontics. The Monobloc was a modification of Ottolengui's removable plate. In 1908, Viggo Andersen developed the Activator appliance. This was the first functional appliance to be widely accepted, especially in Europe. This appliance became the "Norwegian" system of treatment in Orthodontics in the early 1900s.