Immune system refers to the network of all the biological processes that protect an organism from diseases and foreign micro-organisms. It detects a wide range of pathogens, cancer cells and other objects, distinguishes them from the healthy tissues of the organism and responds to them. There are two major subsystems of the immune system, namely, innate immune system and adaptive immune system. Innate immune system relies on the body's ability to recognize the pathogens while adaptive immune response is based on specialized, systemic cells and processes that prevent the growth of pathogens and eliminate them. Immunology is the branch of science that deals with the study of immune systems in all organisms. It has applications in several disciplines of medicine such as oncology, virology, organ transplantation, etc. This book unravels the recent studies in the field of immunology. It presents researches and studies performed by experts across the globe. This book will serve as a reference to a broad spectrum of readers.