Cancer patients exhibit a wide heterogeneity in their responses to chemotherapy. Improvement in chemotherapeutic responses could be achieved by gaining more detailed information on the molecular determinants (i.e., DNA, RNA or protein) underlying this heterogeneity. Pharmacogenomics approaches can be used to integrate information on drug responsiveness with alterations in molecular entities, often on a genome-wide scale. By using information gleaned from pharmacogenomics studies, it is anticipated that cancer chemotherapy can be tailored to the individual patient or tumor phenotype. This review focuses on pharmacogenomics studies conducted to gain insight into the molecular determinants of chemosensitivity to cancer chemotherapeutics.