When determining an orthodontic diagnosis and treatment plan, transverse deviations should be given specific attention. Depending on the structures involved, these issues could have a combination of dental, skeletal, functional, or perhaps a combination of these origins. Determining how the transverse discrepancy interacts with the sagittal and vertical issues is crucial because it frequently affects how a treatment plan is developed. In order to correct a maxillary transverse discrepancy, the palate must often be expanded using both orthodontic and orthopaedic tooth movements. There are now three expansion therapy methods in use: rapid maxillary expansion, slow maxillary expansion and surgically assisted maxillary expansion. This book thoroughly covers the emergence, differential diagnosis, treatment of such issues and the appliances used for the same with clinical implications. It has long been acknowledged that managing transverse discrepancies is one of the most difficult elements of orthodontic treatments.