This book provides information on immunology, which is a branch of biomedical sciences to study the immune system physiology in both diseased and healthy states. Some aspects of autoimmunity enable us to understand that it is not always related to pathology. For example, autoimmune reactions are effective in clearing off the unwanted, excess or aged tissues from the body. Also, autoimmunity occurs after the exposure the non-self-antigen which is structurally similar to the self, assisted by the stimulatory molecules such as cytokines. Therefore, it can be said that there's a minor difference between immunity and auto-immunity. The question of how physiologic immunity changes to pathologic autoimmunity continue to interest researchers. Answer to such questions can be found by understanding physiology of the immune system. This book covers various topics organized under two sections: Nutrition & Immunology and Parasite Immunology. The contributors of this book have carefully selected topics which would be of reader's interests.