This long-term program of research is a fascinating combination of biological and engineering analysis of the mechanics by which food "boluses" (viscous liquids) are transported through the esophagus from the pharynx to the stomach. The esophagus is a muscular organ with both circular and longitudinal muscle layers, the upper 1/3 of which is striated and the lower 2/3 smooth muscle. Food boluses are transported via "peristalsis," the progression of a contraction wave from the upper to lower esophagus. We combine modeling of the fluid motions and stresses with radiographic and manometric measurements within the human esophagus to analyze the mechanical processes important in swallowing and to interpret clinically derived diagnostic information. We have discovered with our modeling that, contrary to popular medical wisdom, separate contraction waves exist in the upper and lower esophagus which must be properly coordinated by the neural control for effective bolus transport. Currently our modeling efforts are directed at the muscle layers within the esophageal wall and its interaction both wit the bolus fluid, and with the central and enteric neurological systems. In a related program we are developing a "Motility Diagnostics System" for application of techniques and tools developed in the course of our research to clinical diagnosis.