Oral appliance therapy is a simple, reversible way for improving snoring and/or obstructive sleep apnea. It may be indicated for the patients who are unable to tolerate continuous positive airway pressure (CPAP) or who have potential risks for surgical intervention. Oral appliance therapy increases airway space by the providing stable anterior positioning of the mandible, pulling out tongue, lifting up soft palate, or changing the muscle activity of the genioglossus. Currently, more than 80 different types of oral appliances have been introduced for snoring and/or obstructive sleep apnea. They are classified by their characteristics such as mode of action, adjustability and material used. This article provides a detailed clinical protocol and treatment procedure for oral appliance therapy.