Myofunctional appliances are mainly used for skeletal correction. As of today, there are various types of myofunctional appliances, but Twin Block is the only removable functional appliance which can be weared 24 hrs. Twin block appliance evolved from the clinical problem of case. Initially, it was for patient with Class II case but as recent advances go on it is proved to be successful in various types of cases.In this book we try to summarize the recent modification of Twin Block appliance according to various cases. We tried to cover modification in all transverse, vertical and sagittal problem.