"Malabsorption" syndrome is the term widely used to describe the end result of either impaired breakdown of nutrients (maldigestion) or defective mucosal uptake and transport of adequately digested nutrients (true malabsorption). The latter may affect a broad range of nutrients (ie, panmalabsorption) or individual nutrients or groups of nutrients (ie, specific malabsorption). This review discusses the etiology and pathophysiology of malabsorption. A diagnostic approach to malabsorption is proposed. Other articles review specific disorders such as celiac disease, bacterial overgrowth, and chronic pancreatitis.