This book describes the significance of the kallikrein-kinin system for kidney function and circulatory regulation, and discusses the role of its regulatory mechanisms. The first part of the book presents the latest highly specific measurement methods that were used as the basis for animal experiments and studies on subjects and patients. For the first time, a reliable determination of the individual components of this system is now available. The second part of the book deals with the physiological importance of the renal kallikrein-kinin system for kidney function and circulatory regulation, while the third part reports on renal and plasma changes in the kallikrein-kinin system in what is likely the largest patient cohort with arterial hypertension to date. This book is intended for the clinical and scientific work of all researchers engaged in this topic.