Bone marrow transplantation, also known as hematopoietic stem cell transplantation, is a medical procedure in which damaged or diseased bone marrow is replaced with healthy stem cells. These stem cells can come from a donor or from the patient themselves, if they have previously collected and stored their own stem cells. Bone marrow transplantation is commonly used to treat various conditions, including leukemia, lymphoma, multiple myeloma, and other blood and immune system disorders. The goal of the procedure is to replenish the patient's blood and immune system with healthy cells, allowing them to recover and potentially be cured of their underlying disease. There are different types of bone marrow transplantation, including allogeneic transplantation (using cells from a donor) and autologous transplantation (using the patient's own cells). The procedure can be complex and carries risks, such as graft-versus-host disease (in allogeneic transplants) and infection. However, for many patients, bone marrow transplantation can offer a chance for a cure or significant improvement in their condition.