Standard treatment of patients with malignant disease has for many years focused on local surgery, radiation, and systemic chemotherapy. Because available therapy has remained unsatisfactory for the more frequent cancers, oncologists have been forced to explore novel therapeutic approaches. The recognition of existing genetic differences between normal and malignant cells as well as progress in immunology, molecular and cellular biology have made preclinical development and clinical application of a variety of gene therapeutic strategies possible, which are highlighted in this article.