Obstructive sleep apnea (OSA) is a common sleep-related breathing disorder, which is characterized by repetitive episodes of complete or partial upper airway collapse during sleep. Maxillomandibular advancement (MMA) is a multilevel skeletal surgery in which the maxilla and mandible are advanced. MMA has been considered as a highly effective surgical therapy for moderate to severe OSA. The overall aim of this thesis is to gain further insight into the role of MMA in treating OSA, which may contribute to the optimization of surgical management of OSA. In chapter 2, there is no significant difference in the effects of MMA on respiratory function and facial esthetics between OSA patients with and without maxillomandibular deficiency. The presence of cardiovascular disease, higher baseline central apnea index, larger superior posterior airway space, and presence of complete anteroposterior epiglottic collapse during drug-induced sleep endoscopy are independently associated with non-response to MMA (chapter 3 and 4). Chapter 5 and 6 compare the clinical efficacy and safety between MMA and other multilevel approaches for OSA, i.e., multilevel surgery and upper airway stimulation, respectively. Additionally, chapter 7 quantifies the degree of the natural intra-individual variation in the upper airway measurements on computed tomography scans at two time points. Chapter 8 reports a patient who was referred for consultation of MMA surgery for severe OSA but was subsequently diagnosed with acromegaly.