Actually, allogeneic hematopoietic stem cell transplantation (AHSCT) is the treatment of choice of malignant hemopathies and also benign hemopathies. AHSCT conditioning presented three main objectives: anti-tumoral effect, immunosuppression and recipient bone marrow elimination. The standard conditioning is homogeneous in intensity but is unfortunately linked to an important toxicity and remains therefore reserved only to young patients. Better understanding of anti-tumoral mechanisms lead to the appearance of non-myeloablative conditioning or reduced intensity conditioning. The reduced intensity conditioning presented a great diversity (lower dose chemotherapy +/- total body irradiation). Many studies showed feasibility, tolerance and efficacy of this type of conditioning. However, this day, none of this conditioning showed his superiority in comparison with the others. Toxicity reduction provides an opportunity to use this approach in more and more old populations who were contraindicated to AHSCT with myeloablative conditioning.