Thrombolytic agents are plasminogen activators that convert the zymogen plasminogen to the active enzyme plasmin, which degrades fibrin. Elucidation of the molecular mechanism of physiological fibrinolysis opened up a new era of fibrin-specific thrombolysis. Fibrin-specific plasminogen activators, including tissue-type plasminogen activator (t-PA), single-chain urokinase-type plasminogen activator (scu-PA) and staphylokinase (Sak), preferentially activate fibrin-associated plasminogen. Generated plasmin remains associated with fibrin, where it is protected from rapid inhibition and can efficiently degrade fibrin, avoiding systemic activation of the fibrinolytic system. Following a decade of clinical investigation t-PA and variants thereof are routinely used for treatment of patients with thromboembolic disease.