Allogeneic hematopoietic stem cell transplantation (HSCT) is the transfer of a hematopoietic and immune system from a healthy donor into a patient as a means of controlling their leukemia, either following initial treatment or relapsed disease. Allogeneic HSCT remains a standard of care across various leukemia subtypes for curative intent. In the year 2020, approximately 22,000 allogeneic transplants were performed in the United States, of which over 5200 were for leukemias [1]. Though the efficacy of allogeneic transplantation is dependent upon numerous factors, graft versus leukemia (GVL) is a critical element. GVL is the process of donor-derived natural killer cells and T lymphocytes exerting anti-leukemic cell activity within the recipient [2]. GVL is also synonymous with graft vs tumor in non-leukemic disease. As the process is mediated by donor immune cells, GVL frequently coincides with alloreactive toxicity against the donor's epithelial cells, resulting in graft versus host disease (GVHD). Here, we provide an overview of the current understanding of GVL following allogeneic HSCT.