Patient response to chemotherapy varies widely between individuals. Pharmacogenetics is the study of inherited DNA polymorphisms that influence drug disposition and effects, the goal of which is the individualization of drug treatment. As unpredictable efficacy and high levels of systemic toxicity are common in cancer chemotherapy, pharmacogenetics is particularly appealing for oncology. Recent studies have shown that polymorphisms in genes involved in drug metabolism, nucleotide synthesis and DNA repair contribute to inter-patient variability in the efficacy and toxicity of many chemotherapy agents. This review will discuss recent developments in the most clinically relevant examples of cancer pharmacogenetics, and how genetic differences among individuals are shaping the future of cancer chemotherapy.