Platelets play key roles in thrombosis and hemostasis by forming aggregates and providing a procoagulant surface, at which thrombin is generated and fibrin fibers are formed. Here we present an overview of the different mechanisms how platelets orchestrate coagulation processes in thrombus formation in thrombosis and hemostasis. Parts of these are via ca2+-dependent activation responses, leading to phosphatidylserine exposure; swelling to form balloons with increased binding of coagulation factors; and calpain-mediated integrin aiibß3 cleavage and inactivation. Other mechanisms are secretion of (anti) coagulation factors, and aiibß3-mediated thrombus retraction, and clot retraction. In a thrombus, coagulation factors are found at both platelets and fibrin fibers. Many of the procoagulant platelet activities are altered in the scott syndrome.