The book is designed as a text to cover essential aspects of immunology in a style that makes the subject most exciting and interesting. Emphasis has been to create an understanding of the principles and applications of immunology. Clinical immunology is the study of diseases caused by disorders of the immune system (failure, aberrant action, and malignant growth of the cellular elements of the system). It also involves diseases of other systems, where immune reactions play a part in the pathology and clinical features. Immunology pervades the activities of most clinicians.