This book intends to report the new progress of studies on urea transporters. 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 report data on urea. Unlike recent physiological books that mostly focus on water and electrolyte physiology，the aim of 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 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 30 years on the 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. This is the 2nd edition of the book. It builds upon the foundational insights of the previous edition, featuring expands content with new chapters and updated chapters to deepen understanding of urea transporters' mechanisms, functions, and significance, reflecting the latest advancements in this research area.