Thrombin is a potent agonist of platelets. In the current article, the research on the interaction of thrombin with blood platelets is reviewed starting with the first studies demonstrating the direct action of thrombin on platelets and ending with an analysis of the importance of the protease-activated receptors (PARs) and the GpIb complex. The antithrombin activity of platelets is discussed in terms of the binding of thrombin to receptor(s) on the platelet surface. Evaluation of the PAR receptors and the GpIb supports a model where thrombin binds to the GpIb receptor prior to the proteolysis of the PAR receptor(s). Thus, the maximal hemostatic response requires both PAR receptors and the GpIb receptors.