The prevalence of allergic and immunological disorders has been steadily increasing in the pediatric population with more than 15% of children affected. However, the number of physicians both treating and investigating immunologic and allergic responses in children remains disproportionately small. Recent advances in our understanding of the immune system, along with the emergence of powerful yet complex research technologies in molecular biology, human genetics and immunobiology have created fertile ground for advancement of understanding of immunological mechanisms but also make it essential for trainees in the fields of allergy, immunology and rheumatology to undergo rigorous training in basic immunology in a cutting edge environment. Such training will prepare young physicians and Ph.D. scientists to advance our knowledge of these diseases through basic research, clinical research and the implementation of novel therapeutic strategies. Equally important, such training will prepare a cadre of physician scientists who will train the next generation of physician scientists. The proposed training program will seek the most talented and committed young pediatricians as well as Ph.D. scientists (all postdoctoral) committed to clinically applicable immunology research and will provide them with intensive training experience in research in an unparalleled environment. All training will be within the general discipline of Immunology, with a broad representation of immunology topics (allergy, tolerance, T cell function, B cell function, autoimmunity, immune regulation and immune deficiency) covered by a diverse and internationally-recognized faculty in the Harvard Medical School community. A three year training experience is proposed; physicians will receive a year one year of clinical training (not funded by this grant) prior to entering the program. The program will fund 9 trainees per year, each with M.D. , M.D., Ph.D. or Ph.D. credentials.