This text is designed for medical and science students taking their first course in immunology and for those wanting to revise their immunological background. Chapters in the "Basic Immunology" section have been updated in the light of recent important breakthroughs in the field. The material covered in the "Immunology in Action" chapters aims to give an insight into the ways in which immunological knowledge has helped not only in the understanding of pathogenesis of infectious diseases, but also in many other medical disciplines.