Suffice it to say that clinical immunology is the immunology of man and his diseases. A clinical immunologist can be identified as that person who is knowledgeable of and skilled in the theories and techniques of immunology and who utilizes these in the investigation or care of patients. The clinical immunologist can be subclassified as a clinician or a clinical pathologist, depending upon whether the chief investment of time of the individual is at the bedside or the bench side. I do not give the clinical investigator a separate category for he generally will fall into either the clinician or the clinical pathologist classification. The disorders to which a clinical immunologist addresses himself fall within the general categories indicated in Table I. The clinical allergist was the first clinical immunologist. He did and has continued to address himself to the classical hypersensitivity diseases, especially the atopic allergies. With the recognition that hematologic, rheumatologic, and renal problems often are of immunologic nature, a broader field of clinical immunology began to emerge, and practitioners and teachers in these three subspecialties had to take on an expertise not previously known to them. The categories designated “immunodeficiency diseases and transplantation” are entirely new categories for clinical medicine, born out of our expanding base of information and capability in the fundamentals of immunology. Cancer is put in parentheses because there has been as yet little impact of the immunology of cancer on management of cancer, a situation which most of us suspect will not last much longer. Finally, I show a miscellaneous group of subspecialties in internal medicine, including gastroenterology, cardiology, and pulmonary diseases, in which the impact of immunology has been restricted to a quite small proportion of the total array of