The mechanisms and physiological functions of urea transporters across biological membranes are subjects of long-standing interests. Although urea represents roughly 40% of all urinary solutes in normal human urine, the handling of urea in the tissues has been largely neglected in the past and few clinical or experimental studies now report data on urea. Most recent physiological text books include chapters on water and electrolyte physiology but no chapter on urea. Our aim in writing this book is to stimulate further research in new directions by providing novel and provocative insights into the further mechanisms and physiological significance of urea metabolism and transport in mammals. This book offers a state-of-the-art report on recent discoveries concerning urea transport and where the field is going. It mainly focuses on advances made over the past 20 years on the biophysics, genetics, protein structure, molecular biology, physiology, pathophysiology and pharmacology of urea transport in mammalian cell membranes. It will help graduate students and researchers to get an overall picture of mammalian urea transporters and may also yield benefits for pharmaceutical companies with regard to drug discovery based on the urea transporter. Baoxue Yang is a professor and vice chairman of the Department of Pharmacology, Peking University. He is also an adjunct professor of Jilin University and a visiting professor of Northeast Normal University. Prof. Yang has been researching urea transporters for nearly 20 years and has published more than 70 original research articles in this field.