Aspirin is the most widely used antiplatelet agent for preventing and treating vascular events. The thienopyridine derivatives, ticlopidine and clopidogrel, are a suitable alternative in patients who are intolerant to aspirin, and clopiclogrel exhibits better tolerability than ticlopidine. The available evidence from randomized trials indicates that dual therapy with clopidogrel and aspirin is modestly but significantly more effective than aspirin in preventing serious vascular events. It is also associated with a favorable benefit-risk profile in patients at high risk (especially in acute coronary syndromes and after stenting). In patients at low risk (stable cardiovascular disease), however, the bleeding risk of dual therapy exceeds its potential benefit. The dose and duration of pretreatment before stenting, the optimal duration of treatment after drug-eluting stent implantation, concurrent administration of platelet glycoprotein IIb/IIIa inhibitors, and the exact mechanism and clinical relevance of clopiclogrel resistance are unclear.