<p>The transfusion of donor lymphocytes after allogeneic stem cell transplantation (known as donor lymphocyte infusion, DLI) is the oldest form of cellular immunotherapy. The therapeutic effect is based on the polyclonal reaction of the transferred immune effector cells of the donor against the underlying malignant disease, the graft versus malignancy reaction (GvM). Based on findings from the canine model, DLI has been used for over 30&#xa0;years, primarily for the prophylaxis and treatment of recurrence of hematological neoplasms after allogeneic transplantation, whereby the various diseases exhibit very different sensitivities to the GvM effect. As a&#xa0;result, both the indications and the potential combination of DLI with classical chemotherapy and newer drugs are different. The main complication of DLI is the induction of a graft versus host disease, the risk of which is influenced in particular by the human leukocyte antigen (HLA) match between donor and recipient as well as the dosage and timing of DLI. Based on large registry data, recommendations for the implementation of DLI in the various constellations and indications have been developed in recent years, which have already proven to be easy to implement in practice. This article summarizes the basic principles, clinical use and recommendations for application.</p>