Pediatric immunology is a recent and important branch of pediatrics. Besides development of vaccines, the discovery of primary immunodeficiencies has represented a major contribution in the history of pediatric immunology. Characterization of these disorders as inborn errors of immunity has been crucial for understanding the functional organization and ontogeny of the immune system. Thus, progress in the study of immunodeficiency diseases has contributed to progress in pediatric immunology as a whole. As a result of these advances and a major biotechnology breakthrough, new therapeutic strategies have been devised. The benefits of these strategies extend far beyond the area of immunodeficiencies; they permit better care of infants and give new therapeutic approaches to other inherited disorders.