When Shaul Massry and Herbert Fleisch asked me to write a foreword for this book, I was honored and eagerly looked forward to reading the many chapters. As they came and I skimmed through them, my mind wandered back to the earliest classic contributions in this field in the late 1920s and early 1930s by Albright and his associates, Greenwald and Gross and Adolph, on the homeostatic regulation of inorganic phosphate and the central role of parathyroid hormone (PTH) in this regulation. They clearly showed the exquisite sensitivity of the renal handling of phosphate to varying dietary and parenteral loads and to changes in the level ofPTH. That two outstanding investigators in the field of divalent ion me­ tabolism should choose to edit a book solely about the renal handling of inorganic phosphate shows how far we have progressed from these early classics to the recent almost exponential increase in the research and publications related to this subject. Despite this increase, I asked myself, is such a large new monograph, consisting of 13 chapters and 30 distin­ guished authors, warranted? My reading of these chapters and my learning so much from them convinced me that it is, and my pride was heightened in being asked to write the foreword for this book.