The gradual decline in the functioning ability of the immune system to respond to the pathogens, brought on by natural age advancement is called immunosenescence. It includes a decline in the host's capacity to respond to infections and the deterioration of the development of long-term immune memory. It is a major cause of increased frequency of morbidity and mortality among older adults. It may result due to unavoidable exposure to a wide variety of antigens, including virus and bacteria. It is believed that a decline in the hormone levels with advancement in age is also responsible for weakened immune responses in aging individuals. This book includes some of the vital pieces of work being conducted across the world, on various topics related to the immunology of aging. It aims to shed light on some of the unexplored aspects of the immunology of aging and the recent researches in the subject. The extensive content of this book provides the readers with a thorough understanding of the subject.