Urokinase-type plasminogen activator (uPA) is a serine protease involved in tissue remodeling and cell migration. At the gene level, the interplay between a complex enhancer, required for induced and basal transcription, and the minimal promoter finely tunes uPA expression. The active form of uPA is bound to its high affinity receptor on the cell surface, where specific inhibitors modulate its enzymatic activity. Such inhibitors also regulate the cell surface levels of uPA by triggering the internalization of the uPA-receptor-inhibitor complex. The role of uPA is not only linked to its action as an enzyme. In fact, the mere binding of uPA on the cell surface also brings about two events that broaden the spectrum of its biological functions: (1) a conformational change of the receptor, which, in turn, affects its interaction with other proteins; (2) a signal transduction which modulates the expression of apoptosis-related genes. Besides its applications as a thrombolytic agent and as a prognostic marker for tumors, uPA may provide the basis for other therapies, as the structure of the receptor-binding domain of uPA has become a model for the design of anti-cancer molecules.