Orthodontic appliances are the appliances created by orthodontic technology that is used for the treatment of malocclusions. There are two main types of orthodontic appliances: active and functional. They can either be fixed or removable appliances. The active appliance is the tool that is used to apply forces to the teeth in order to change its relation. Some examples of fixed orthodontic appliances are begg light wire appliances, bi helix, self-ligating edgewise appliances, tri helix, pre-adjusted edgewise appliances etc. The functional orthodontic appliance is used to produce orthodontic forces by utilizing the muscle action of the patient and responses of the nervous system. Some examples of fixed orthodontic functional appliances are herbst appliance and twin block appliance. This book provides comprehensive insights into the field of fixed orthodontic appliances. It covers in detail some existent theories and innovative concepts revolving around this domain. Researchers and students in this field will be assisted by this book.