After more than a decade of unfulfilled promises, radioimmunotherapy for the treatment of non-Hodgkin’s lymphoma has been demonstrated to be efficacious in the treatment of refractory disease. It is likely that in the near future, the Food and Drug Administration will approve one or more radioimmunoconjugates for clinical use. However, the optimal use of the agents in the treatment of non-Hodgkin’s lymphoma remains to be defined. The role for these drugs is influenced by the target antigen as well as the radionuclide. In this review, the biologic principles, seminal clinical results, and avenues for future development of RIT are discussed.