Knowledge of the juxtaglomerular apparatus (JGA) of the kidney and of the synthesis and secretion of renin has increased to such an extent over the past few years that it is now appropriate to summarize this knowledge in a monograph on the JGA, the first of its kind. It was the authors' special concern to demonstrate the association between structure and function for renin secretion, not only within the juxtaglomerular region, but also in the region of the renal cortex beyond the JGA. The description of the pathology of the human JGA, studded with references to experimental findings but nevertheless fully self-contained, should help to make this monograph also useful for clinicians.