The immune system is the body organ that protects all higher organisms against infections and parasites. The immune system of vertebrates is particularly complex and is one of only two immune systems which allows - in the form of antibodies - for almost unlimited variability through genetic rearrangements. Almost any disruption in the immune system results in a more or less severe disease and/or will render the carrier susceptible to a variety of infectious agents. In addition, it has become clear that the immune system often plays a critical role during cancer development and an inappropriate immune response is responsible for the development of autoimmune diseases and allergies.

Understanding the immune system is thus not only critical for the treatment of many infectious diseases but also for the treatment of autoimmune diseases, allergies and increasingly cancer.

This concise introductory textbook uses carefully chosen examples from clinical and experimental observations to provide an insight into the principles underlying the immune system. As a result, it encourages readers to ask critical questions in order to further advance our understanding of this unique organ. Both authors are experienced lecturers and highly regarded researchers.