Clopidogrel is the most widely used thienopyridine in cardiovascular patients. Its indications include acute coronary syndromes and stenting, in association with aspirin. In stable atherothrombotic patients, clopidogrel is a valuable alternative to aspirin. Studies have shown an association between the biological response to a loading dose of clopidogrel and clinical events after stenting. This variability of the biological response is probably multifactorial (compliance, genetics, weight, drug interactions). Several aspects, such as the lack of standardized tests, of validated cut-offs to define resistance and of alternative treatments with proven efficacy in case of a biological resistances, do not currently allow performing these tests in everyday care and limit their use in the clinical research setting.