The term “tandem” is used to imply that both maxillary and mandibular dentitions are affected simultaneously by the mechanics. The mechanics have been shown to be effective in the treatment of transverse maxillary deficiency, arch length insufficiency, Class II jaw and tooth relationships, and anterior skeletal overclosure and dental overbite. The treatment is growth-coupled and, therefore, most effective during the transitional and early full permanent dentition period of growth and development. With modification, it can be effective in the latent grower and the nongrower. The mechanics are designed to hold the buccal teeth in space, while the incisors are advanced with the growth of the jaw. Thus, space is gained between the molars and incisors without changing the buccolingual or labiolingual tooth-muscle relationships. This may be the reason these mechanics have produced stable results. World J Orthod 2003;4:109–118.