When Arthur Vander wrote the first edition of this text about the kidneys over 3 decades ago, much was known about what the kidneys do; much less was known about how the kidneys do it. Research in the intervening years has revealed insights into renal mechanisms, but also raised new questions. As the research community continues to provide new details of the intricate workings of the kidneys, the difficulty of the task facing the student of renal physiology increases in parallel. That task is to keep sight of overall renal function within a cloud of cellular and molecular details. The purpose of this text is to obviate much of that difficulty by connecting purpose with mechanism, that is, to focus on “big picture” and limit the amount of detail. The text stresses 2 things: the goals of renal processes so that there is context for a given renal activity, and the logic behind renal processes, with attention given to aspects that experience tells us are sticking points for students. Thus, the text includes considerable background material that goes beyond strictly renal mechanisms. In preparing this revision of the text, we scoured the research literature dealing with the kidney in order to make the text consistent with current views on renal mechanisms. We revised all sections of the text to bring them up to date. More importantly we extensively reworded explanations to make them as logical and clear as possible. This includes replacing or revising many of the figures. We have provided several aids to help the reader. First, each chapter includes a list of key concepts with indicators in the text where those concepts are presented. Second, there are boxed statements scattered throughout the text to help emphasize major points. Third, there are study questions at the end of each chapter, with an answer key and explanations of the answers at the end of the book.