In recent years there has been a dramatic increase in developing gene therapy approaches for the treatment of cancer. The two events that have permitted the formulation of concept of cancer gene therapy are the new understanding of the molecular mechanisms underlying oncogenesis, and the development of the DNA-delivery vehicles or vectors. Many approaches to cancer gene therapy have been proposed, and several viral and non-viral vectors have been utilized. The purpose of this review article is to describe the various strategies of cancer gene therapy (transfer of tumor suppressor genes, suicide genes-enzyme/pro-drug approach, inhibition of dominant oncogenes, immunomodulation approaches, expression of molecules that affect angiogenesis, tumor invasion and metastasis, chemosensitization and radiosensitization approaches, and chemoprotection of stem cells). The chapter also reviews the commonly used vectors (retroviral vectors, adenoviral vectors, adeno-associated viral vectors, pox viruses, herpes simplex viruses, HIV- vectors, non-viral vectors and targetable vectors) for cancer gene therapy. Some of the important issues in cancer gene therapy, and the potential future directions are also being discussed.