This textbook submits the modern data on all aspects of structure and functions of the immune system in norm and pathology. The most recent knowledge about innate immunity and the mechanisms of generation of adoptive immunity is presented at the organismic, cellular and molecular genetic levels. The information about the immune cell populations, the structure of immunocyte receptors, the intracellular signaling pathways, major histocompatibility complex, immunity genetic control, immunologic memory is given. The immune deficiencies, allergic and autoimmune diseases are reviewed. The possibility of phenotypic correction of genetically controlled immunity by the immunotropic drugs is shown. The textbook is supplied with the test examination program on CD. The textbook is intended for students, postgraduates, lecturers, practical physicians and scientific researchers engaged in various fields of medicine and biology.