The term "functional appliance" refers to a variety of appliances designed to alter the arrangement of various muscle groups that influence the function and position of the mandible in order to trasmit forces to the 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.A number of functional appliances have been developed, since the time of the "activator" developed by Andresen which offer definite advantages in growth modification to correct skeletal malocclusions. To overcome the disadvantages of removable appliances fixed functional were introduced. They are the appliances which are used to correct Class II malocclusion. This book encompasses a brief description of all fixed functional appliances.