There are at least eight mechanisms identified that result either in volume clearance of the pharynx and esophagus (secondary peristalsis and pharyngeal swallow) or prevent entry of the gastric content into the esophagus and pharynx (LES and UES), accentuate these barriers (esophago-UES and pharyngo-UES contractile reflexes), or induce closure of the vocal cords and introitus to the trachea (esophagoglottal and pharyngoglottal reflexes). The sum effect of various combinations of these mechanisms is suggested to help prevent retrograde aspiration. In other words, airway protective mechanisms against retrograde aspiration are multifactorial and involve delicate interaction between upper GI and upper airway tracts. Although the existence of these mechanisms in normal volunteers has been documented, their function in patients with retrograde aspiration and supraesophageal complications of gastroesophageal reflux disease currently awaits investigation.