Many advances in vitamin D physiology and biochemistry have been made in recent years. Vitamin D metabolites and analogs have found increasing application in clinical medicine. The purpose of this text is to review what is known about vitamin D physiology and draw attention to areas of vitamin D research that have changed within the last 2-3 years. Additionally, information concerning clinical aspects of vitamin D is also presented. More than 40 scientists have generously contributed chapters to this text; I thank them for their efforts. As might be expected, not everyone has the same point...