Functional appliances are considered to be primarily orthopedic tools to influence the facial skeleton of the growing child in the condylar and sutural areas. All functional appliances take advantage of interaction between mechanical function and morphologic pattern and use common mechanisms of bone turnover, rhythm, activation, resorption, and formation for their action.These effects are produced because of their ability to alter the stomatognathic muscle balance. For growth modification, functional appliances transmit forces (from muscles or viscoelastic stretch of soft tissue) to the condylar region and thereby, inducing new bone formation or glenoid fossa remodeling.Treatment of class II malocclusion has always been an enigma to the orthodontic faternity. Skeletal class II malocclusion has been treated by various forms of functional appliances to achieve better esthetics and functional harmony. Correction of skeletal class II malocclusion by growth modulation during active growth can be achieved using various myofunctional appliances like activator, Frankel's regulator and the twin block. This book summarize about each appliance with their efficacy in detail.