In the last two decades, new developments in haploidentical hematopoietic stem cell transplantation have made it a viable alternative donor option. Initially, allogeneic HSCT was limited to patients who had HLA-identical related donors. To provide options for patients lacking a matched related donor, registries of unrelated volunteer donors or cord blood units have been established with the hopes of providing a phenotypically well-matched stem cell product. The use of haploidentical donors broadens the application of HSCT more than these other approaches. In addition, the greater HLA mismatching associated with haploidentical HSCT may potentiate graft versus tumor (GVT) effects.