When Glu-plasminogen, the native circulating form of the zymogen, is bound to cell surfaces, its activation is markedly enhanced compared with the reaction in solution. This results in localization of the broad-spectrum proteolytic activity of plasmin on cell surfaces. The cell-associated plasmin plays a key role in fibrinolysis, cell migration, and prohormone processing. It is well established that the localization of plasminogen and plasminogen activators on cell surfaces promotes the enhanced plasminogen activation on the cell surface. The focus of this article is to review recent studies demonstrating that the conversion of Glu-plasminogen to the more readily activated Lys-plasminogen derivative is necessary for optimal stimulation of plasminogen activation on the cell surface, and that the interaction of Glu-plasminogen with cells serves to increase processing of Glu-plasminogen to Lys-plasminogen, thereby enhancing plasminogen activation on the cell surface.