GvHD prevention without compromising the graft versus malignancy potential or the immunodefence against infectious agents is the art of allogeneic hematopoietic cell transplantation. This book summarizes state-of-the-art GvHD preventive strategies based on animal models and clinical trials. It focuses on novel approaches as well as important supportive measures with relevance for clinical practice. This critical overview is intended for transplant specialists as well as novices and colleagues taking care of patients in the field of hematopoietic cell transplantation.