Impedance monitoring was first proposed as a method for gastrointestinal motility 10 yr ago. It detects changes in resistance to current flow when a bolus traverses an electrode pair, and can distinguish liquid (low-impedance) from gas (high-impedance) boluses (1). Electrode pairs placed at multiple sites on a standard solid-state esophageal manometry catheter can track antegrade bolus transit through the esophagus to correlate with manometry findings. In contrast, the electrode pairs placed at multiple sites on a standard pH probe can track retrograde bolus transit from the stomach to the esophagus to correlate with pH. This issue of The American Journal of Gastroenterology contains reports that relate to each of these two distinct applications of impedance monitoring.