The development of miniaturized electronic pressure transducers and portable digital data recorders with large storage capacity has made ambulatory monitoring of esophageal motor function over an entire circadian cycle possible. The broad clinical application of this new technology in a large number of asymptomatic normal volunteers and patients with primary esophageal motor disorders or gastroesophageal reflux disease provides new insights into esophageal motor function in health and disease under a variety of physiologic conditions. In normal volunteers and symptomatic patients, esophageal motor activity increases with both the state of consciousness and eating activity, i.e., from sleep to awake to meal periods. In the normal situation there is a higher prevalence of nonperistaltic esophageal contractions than appreciated on stationary manometry. Compared with standard manometry, ambulatory esophageal manometry provides a more than 100-fold larger database for the classification and quantitation of abnormal esophageal motor function and leads to a change in the diagnosis in a substantial portion of patients with symptoms suggestive of a primary esophageal motor disorder. In patients with nonobstructive dysphagia, the circadian esophageal motility pattern is characterized by an inability to organize the motor activity into peristaltic contractions during meal periods. In patients with noncardiac chest pain, ambulatory motility monitoring can document a direct correlation of abnormal esophageal motor activity with the symptom and shows that the abnormal motor activity immediately preceding the pain episodes is characterized by an increased frequency of simultaneous, double- and triple-peaked, high-amplitude, and long-duration contractions. A long esophageal myotomy can abolish the ability of the esophagus to produce this abnormal motor pattern. In patients with gastroesophageal reflux disease, ambulatory motility monitoring shows that the contractility of the esophageal body deteriorates with increasing severity of esophageal mucosal injury, compromising the clearance function of the esophageal body. These data suggest that ambulatory esophageal motility monitoring allows for a more precise classification of esophageal motor disorders than standard manometry and can identify abnormal esophageal motor pattern associated with nonobstructive dysphagia, noncardiac chest pain, or gastroesophageal reflux. Ambulatory esophageal manometry therefore should replace standard manometry in the assessment of esophageal body function and has potential to improve the diagnosis and management of patients with esophageal motor abnormalities. The combination of ambulatory 24-hour esophageal manometry with esophageal and gastric pH monitoring is currently the most physiologic way to assess patients with functional foregut disorders.