This is the fourth edition of a text that first appeared in 1976. At its inception it measured 471 pages; the current edition has 846 pages, a remarkable 80% growth in size. However, the physical arrangement and scope of nephrologic topics covered in the fourth edition is virtually identical to the first, and the book retains its original compact feel. The given purpose of this text is that the reader will understand the pathophysiology of kidney disease. I believe that the authors have been very successful in achieving this goal. Eleven new names appear on the list of contributing authors. Three chapters (Disorders of the Renin-Angiotensin-Aldosterone System, Obstructive Nephropathy: Pathophysiology and Management, and Proteinuria and the Nephrotic Syndrome) have been freshly rewritten by acknowledged experts in these areas. As with the other chapters, the format of the new ones is an initial well-referenced description of the pathophysiology of the disorder,