The UDP-glucuronosyltransferases (UGTs) are a superfamily of “drug metabolizing” enzymes that catalyze glucuronidation. This process facilitates the biological inactivation and excretion of noxious chemicals, such as carcinogens and therapeutic drugs, as well as endogenous compounds such as bilirubin and steroids. Traditionally, human UGTs were thought to act primarily within the context of hepatic metabolism, however recent evidence suggests these enzymes are widely expressed in extrahepatic tissues and contribute significantly to glucuronidation capacity. This book summarizes the characterization of genetic factors that regulate UGT transcription in extrahepatic tissues, with a specific focus on the prostate-enriched UGT2B17 gene and three closely related gastrointestinal-enriched genes UGT1A8, UGT1A9 and UGT1A10. These findings have implications for our understanding of how glucuronidation is physiologically controlled as well as how it varies between individuals. This book would be of particular interest to scientific professionals wishing to gain a general overview of the genetic regulation of drug metabolizing enzymes.