In the processes of hemostasis and thrombosis, platelet activation and coagulation are highly entangled by jointly regulating the formation of clots or thrombi. In this overview, we describe current knowledge on platelet interactions in the phases of coagulation and thrombus formation. Addressed are the roles of platelets in the extrinsic (via tissue factor and factor VII) and intrinsic (via factor XII and prekallikrein) triggering of coagulation. Furthermore, the contribution of platelets in the common coagulation pathway, thrombin generation with feeding loops, involving factors V, VIII, IX, X, and XI. Additional topics are the targets of thrombin on platelets, the mechanisms of formation and dissolution of fibrin clots, and the unique properties of populations of phosphatidylserine-exposing, coated, and contracting platelets. Further discussion is how protease-activated receptors (PARs), glycoprotein VI (GPVI), GPIb-V-IX, integrins, and granule secretion steer the coagulation. Final discussion elements are the roles of platelets in natural anticoagulation via protein C and S, tissue factor pathway inhibitor, and serpins; and the essential fibrinolysis process in clotting of plasminogen activation and serpin-mediated plasmin modulation. This current knowledge provides openings for novel patient treatments interfering with the platelet-controlled coagulation.