Plasminogen activator inhibitor-1 (PAI-1) is the primary physiological inhibitor of both tissue-type plasminogen activator (t-PA) and urokinase-type plasminogen activator (u-PA) and is consequently one the most important inhibitors of the plasminogen/plasmin system. PAI-1 attenuates fibrinolysis and increased levels of active PAI-1 have been associated with an increased risk for cardiovascular diseases. PAI-1 knock-out mice as well as PAI-1 overexpressing mice have been generated and characterized to study the role of PAI-1 in vivo. A number of PAI-1 inhibitors have been generated to study the pharmacological effect of PAI-1 inhibition in vitro and in vivo. The current review provides an overview of 1) the biochemical features of PAI-1, 2) the role of PAI-1 in diverse pathologies, 3) the in vitro and in vivo data obtained with PAI-1 inhibitors and 4) the vitronectin, glycosylation and species dependency of PAI-1 inhibition.