Interindividual variability in the efficacy and toxicity of chemotherapy is associated with polymorphisms in genes encoding drug-metabolizing enzymes, transporters, or drug targets. Pharmacogenomics is the study of the hereditary basis of these interindividual differences and aims to identify genetic factors to predict toxicity and therapeutic outcomes. There exist several clinically relevant examples of the utility of pharmacogenomics that associate specific genetic polymorphisms in drug metabolizing enzymes and drug target enzymes. This review discusses the current and future applications of pharmacogenomics in clinical cancer therapy.