This book is a comprehensive review of thrombin, especially as regulatory protease. The ready availability of highly purified thrombin has stimulated rapid advances in the cell biology of this important macromolecule. The text focuses on research findings from the discovery of thrombin by Andrew Buchanan in 1842 to the present. A substantial amount of this work was conducted by the author and his colleagues. His work on the purification of thrombin was seminal to much subsequent work on thrombin. This volume provides a framework for future studies now made possible by the discovery of the importance of exosites in the physiology of thrombin function. The current work describes the process of the development of an oral inhibitor of thrombin used in the prevention of thrombosis. Key Features Reviews the history of Thrombin (Fibrin Ferment) Documents the relation of protein engineering and chemical modification in the study of thrombin Summarizes the interaction of thrombin with fibrinogen and fibrin Outlines the role of exosites in thrombin function Describes the development of an oral inhibitor for thrombin.