Oral appliances act by keeping the mandible and/or the tongue forward to enlarge the upper airway and reduce pharyngeal collapsibility. It is recommended that a custom, titratable appliance is used for treatment and mandibular advancement appliances (MAA) are usually preferred. Stabilizing the mandible, minimizing the vertical opening, and titrating the mandibular protrusion according to disease severity are important factors in the success of treatment. MAAs are indicated in adult patients with primary snoring or for OSA patients who are intolerant of continuous positive airway pressure (CPAP) therapy or prefer alternative treatments. The contraindications are insufficient number of teeth, untreated periodontal disease and mobile teeth, active temporomandibular disorder (TMD), and inability to advance the mandible more than 6 mm. Oral appliance therapy requires the sleep physician and the dentist working as an interdisciplinary team. Some possible side effects may involve the appliance, the teeth, temporomandibular joint, masticatory muscles, soft tissues, and the bony structures. Most of these are mild and transient. Although CPAP is more successful in improving polysomnographic variables, MAAs achieve significant improvements in health outcomes, symptoms, and quality of life comparable to CPAP. These improvements are possibly due to higher compliance to MAA therapy. Timely management of side effects, patient participation in treatment, and improved prediction methods is necessary to improve long-term adherence. Unfortunately, predictors of treatment success to determine who would respond to oral appliance therapy are currently limited.