All the functional appliances have been designed to treat all types of malocclusion, they are most effective in treating dental and skeletal class II malocclusion, particularly in cases with mandibular deficiency. The goal of myofunctional appliances is to use functional stimulus, channeling it to the greatest extent that the tissues, jaws, condyles and teeth allow.The age at which functional appliance therapy is instituted is of major importance for the successful correction of malocclusions. Functional appliance treatment should be coincident with periods of active growth. Most agree that it should be initiated during the middle to late mixed dentition i.e. at the age of 9 to 12 years. It can also be used earlier if the patient can cooperate in wearing the appliance. Myofunctional appliances can be seen as an exerciser for elimination of habits that may cause malocclusion or as appliances helping orthodontic treatments and they should be given at the right age, so the maximum utility of the growth can be achieved. This book will help in understanding the fabrication, function, mechanism of action and effect of myofunctional appliances.