Adoptive T cell immunotherapy is the isolation of tumor-specific T cells from a cancer patient, in vitro activation and expansion of these T cells, and re-infusion of the T cells to the patient. In a small percentage of patients with tumor types susceptible to immune modulation, adoptive therapy has proven to be highly effective. The use of adoptive therapy has several limitations which are being actively investigated today. T cells from various sources are being isolated for adoptive therapy: lymphocytes can be isolated from tumor lesions, from lymph nodes draining the tumor or a tumor vaccine site, or from peripheral blood lymphocytes stimulated with tumor antigens in vitro. Recent advances in T cell therapy include enhanced efficacy of T cell therapy following non-myeloablative chemotherapy and genetic modification of T cells for use in adoptive therapy. Clinical trials using gene-modified T cells with improved activation, lifespan, and tumor targeting are on the horizon. It is likely that adoptive immunotherapy will remain a fertile area for investigation resulting in advances in the fields of T cell biology and gene therapy. Adoptive therapy for cancer will become widespread only after its clinical benefit for sizeable patient populations has been established.