Graft vs host disease is a serious immunological complication of allogeneic haematopoietic cell transplantation, leading to a significant morbidity and mortality. It occurs when donor T lymphocyte react to foreign host cells. The physiopathology is a more complex process implicating host tissues damage caused by the conditioning regimen, cytokines, cellular effectors implicated in the immune response such as donor lymphocytes T, antigen presenting cells and mechanisms of apoptosis. This review focuses on the physiopathological basis, risk factors, clinical aspects; prevention and current management strategies to treat graft vs host disease. Recent developments in our understanding of this bone marrow transplantation complication have profoundly influenced the practice of allogeneic haematopoietic cell transplantation. There is a growing realisation of the importance of a graft vs leukaemia effect, strategy, which has encouraged the development of less conditioning regimens. Segregation between graft vs host effect and graft vs leukaemia effect is a key challenge, and could lead to new efficient and specific immunotherapy.