Primary immunodeficiencies, also commonly called inborn errors of immunity (IEI), are commonly due to developmental or functional defects in peripheral blood cells derived from hematopoietic stem cells. In light of this, for the past 50 years, hematopoietic stem cell transplantation (HSCT) has been used as a definitive therapy for IEI. The fields of both clinical immunology and transplantation medicine have had significant advances. This, in turn, has allowed for both an increasing ability to determine a monogenic etiology for many IEIs and an increasing ability to successfully treat these patients with HSCT. Therefore, it has become more common for the practicing allergist/immunologist to diagnose and manage a broad range of patients with IEI before and after HSCT. This review aims to provide practical guidance for the clinical allergist/immunologist on the basics of HSCT and known outcomes in selected forms of IEI, the importance of pre-HSCT supportive care, and the critical importance of and guidance for life-long immunologic and medical monitoring of these patients.