Oral appliances are increasingly gaining a place in the treatment of sleep disordered breathing caused by upper airway obstruction. This review of publications since 1995 documents substantial progress in the scientific basis for this therapy. Imaging by several techniques has shown that mandibular advancing oral appliances open the airway in awake and anaesthetized subjects, creating the presumption that this effect is maintained in sleep. Three controlled cross-over treatment trials have shown that patients consistently prefer oral appliance over continuous positive airway pressure therapy, especially when the treatment effect is strong. Appliance design and use indicates a preference for adjustable mandibular advancing appliances. Complications of therapy appear to be infrequent, but evidence for safety of long-term use is still limited. Oral appliance therapy can be an effective therapy for sleep disorders caused by upper airway obstruction. Considering the accumulated evidence, it is no longer tenable to label oral appliance therapy an OexperimentalO procedure.