Allogeneic haematopoietic stem cell transplantation is today an important therapeutic procedure in the treatment of many malignant and non – malignant haematological and non – haematological diseases. The main purpose of such treatment is to replace the recipient’s ill or dysfunctional bone marrow with healthy donor's haematopoietic stem cells. In addition to being an important prerequisite for successful transplantation, matching in the human leukocyte antigen system (HLA system), it is also important to implement the correct conditioning regimen as part of the patient's pre – transplant preparation. There are two main types of haematopoietic stem cell transplantation – autologous (where the donor and the recipient are the same person) and allogeneic (where the donor and the recipient are different people). While in the past the main source of haematopoietic stem cells was bone marrow, today more and more haematopoietic stem cells are taken from peripheral blood which is a much safer and painless approach for the donor. The donor for allogeneic transplantation can be related or unrelated, HLA – matched or HLA – mismatched. The best outcomes of transplantation are achieved from HLA – matching related donor, but very small number of patients has such a donor, so the need to open Registers of voluntary (unrelated) haematopoietic stem cell donors has developed worldwide and to develop protocols that will enable favorable transplant outcomes using transplants from HLA – mismatched donors. Today, there are three protocols that allow us to circumvent the historical barriers of haploidentical haematopoietic stem cell transplantation, each with its advantages and disadvantages – T – cell depletion with „megadose“ CD34+ cells (TCD protocol), granulocyte colony – stimulating factor – primed allografts combined with intensive pharmacological immunosuppression (GIAC protocol) and high – dose, post – transplantation cyclophosphamide (PTCy protocol).