The upper airway has long been an area of interest in orthodontics. Normal airway is one of the important factors for the physiologic growth of the craniofacial structures. Clinicians and researchers involved in the treatment of dentofacial deformities have long searched for determinants of facial morphology. Since the turn of the century, compromised airway function has been implicated as an etiologic factor in dentofacial development. Certain malocclusions may have some association with airway problems in some children. Upper airway research has allowed us to begin to understand the biomechanical basis for obstructive sleep apnea syndrome as well as mouth breathing. Modern developments in imaging have brought forth many distinct know-hows and methodologies. This book deals with the basics of airway through an orthodontist's perspective.