Although obstructive sleep apnea is a highly prevalent disorder with significant clinical consequences and major public health ramifications, we understand little about its pathogenesis. Upper airway imaging, however, has allowed us to begin to understand the biomechanical basis for obstructive sleep apnea and the mechanisms underlying the efficacy of various therapeutic interventions. Imaging techniques can provide high-resolution anatomic data on the structure and function of the upper airway and surrounding soft-tissue structures. MR and CT tomography imaging allow precise anatomic evaluation of the airway and surrounding soft-tissue structures (examination of the “donut” rather than the “hole in the center of the donut”). In addition, dynamic and state-dependent imaging techniques provide information on the soft-tissue and bony structures, the motion of which underlies the dimensional changes that take place in the upper airway during respiration, sleep, and airway closure. Upper airway imaging is a powerful research technique that has significantly advanced our understanding of the biomechanics, pathophysiology, and treatment of obstructive sleep apnea. Moreover, clinical indications for upper airway imaging in patients with sleep apnea are beginning to evolve.