The indication for allogeneic stem cell transplantation (allo-SCT) have been expanded nowadays because many stem cell sources became available and new conditioning procedures such as reduced intensity stem cell transplantation (RIST) have been developed. Stem cell sources can be classified into bone marrow cells, peripheral blood stem cells, cord blood cells and every source derived from related or unrelated donors. Also, HLA mismatched transplantation has been studied especially in haploidentical donors. Now we must select the most compatible stem cell source for the recipient condition and disease status. RIST has expanded the indication of allo-SCT because of low regimen related toxicity. However, evaluation of graft versus leukemia (GVL) effect and control of graft versus host disease (GVHD) are still unresolved problems. Further investigations of the therapy of chronic GVHD and other posttransplant problems are warranted to improve the outcome and quality of life of the patients.