The immune system refers to the network of biological processes that protect an organism from diseases. It recognizes and reacts to a wide range of pathogens including cancer cells, viruses and parasitic worms. The immune system is divided into two main subsystems, namely, the adaptive immune system and the innate immune system. The adaptive immune system recognizes the unique components of individual pathogens, whereas innate immune system recognizes the components shared by all pathogens. Antigens are the type of substances that are identified by the immune system and can subsequently trigger an immune response. A dysfunctional immune system can lead to cancer, autoimmune diseases, and inflammatory diseases. Immunodeficiency is caused when the immune system is not active, which leads to persistent and potentially fatal infections. This book is compiled in such a manner, that it will provide in-depth knowledge about immuno systems biology. It will prove to be immensely beneficial to students and researchers in this area of study.