AbstractInborn errors of immunity (IEI) comprise diseases arising from genetic defects that lead to abnormalities in immune cell development or function with a wide spectrum in severity and clinical manifestations. The number of transplants for IEI has increased significantly over the last years, elicited by better insight in the pathogenesis of the IEI (and thus the “curability” of these diseases with allo-HCT), better outcomes even with unrelated and haploidentical donors, and more differentiated approaches to HCT including reduced toxicity conditioning regimens.