Acute coronary syndromes (ACS) remain life-threatening disorders that are associated with high morbidity and mortality. Dual-antiplatelet therapy with aspirin and clopidogrel has shown to reduce cardiovascular events in patients with ACS. However, there is substantial inter-individual variability in response to clopidogrel treatment in addition to prolonged recovery of platelet reactivity as a result of irreversible binding to P2Y12 receptors. This high inter-individual variability in treatment response has primarily been associated with genetic polymorphisms in the genes encoding for cytochrome (CYP) 2C19 that affect clopidogrel’s pharmacokinetics. While FDA has issued a boxed warning for CYP2C19 poor metabolizers due to a potentially reduced efficacy in these patients, results from multivariate analyses suggest that additional factors, including age, sex, obesity, concurrent diseases and drug-drug interactions, may all contribute to the overall between-subject variability in treatment response. However, the extent to which each of these factors contributes to the overall variability and how they are interrelated is currently unclear. The objective of this review article is to provide a comprehensive update on the different factors that influence clopidogrel’s pharmacokinetics and pharmacodynamics and how they mechanistically contribute to inter-individual differences in response to clopidogrel treatment.