The benefits of Clopidogrel on the treatment of acute coronary syndromes are well established. However, not all patients respond in the same way to Clopidogrel therapy, and there are patients who suffer major adverse cardiovascular events despite being on treatment, emerging the concept of Clopidogrel resistance. This book focuses on this topic, mainly in the definition, response assessment, clinical implications, patients' management and emerging therapies (prasugrel, cangrelor and ticagrelor).