The classification of the unstable angina syndrome has represented one of the main objectives of the cardiologists in the two last decades. The ambiguous definition of this syndrome has led to the phenomenon that numerous classifications have been achieved, based especially in the different clinical presentations of this syndrome, that are neither clearly matched with a different physiopathology nor with the prognosis. On the other hand, the validation of the majority of the classifications have been attempted through studies of selected populations with an insufficient number of patients in a syndrome with a wide spectrum of clinical presentation, pathophysiology and prognosis. On this basis, the existing classifications do not fully satisfy the scientific community, which is confirmed by the periodical appearance of new proposals. In our setting, the classifications which are most applied are those of the Spanish Society of Cardiology and Braunwald's Classification. Both offer the usefulness of their simplicity, since they only consider clinical aspects, but sustain the previously mentioned inconveniences. A more practical classification could possibly be based exclusively on physiopathological or prognostic characteristics, which allow a more adequate management of these patients.