Adoptive T-cell therapy involves the passive transfer of antigen-reactive T cells to a tumor-bearing host in order to initiate tumor rejection. Based upon animal models, effector T cells with tumor-specific reactivity are superior to non-specific effector T cells in mediating tumor regression in vivo. Both CD4+ and CD8+ T cells are capable of initiating tumor rejection after adoptive transfer. Several different culture methods have been reported that permit in vitro expansion of immune T cells while retaining tumor specificity. The ability to generate human tumor-specific effector T cells capable of mediating tumor rejection in vivo has provided tools to identify tumor-associated antigens. Future directions in this field involve the selective isolation and expansion of subpopulations of T cells critical to initiating tumor rejection, and the use of molecular techniques to generate effector T cells.