Contents:1. Introduction 2. Immune System Simulating Body System 3. Historical Perspective 4. Immune System 5. Organization of Lymphoid Tissue 6. Mechanism of Protection to Foetus and New Borne 7. Players of Immune System 8. Host Parasite Arm Race 9. Accessory Molecules (Cytokines) 10. Immunity 11. Different Components of Protection 12. Specific Immune Response 13. Immunoprophylaxis (vaccines and Antisera) 14. Unique Operation that Make Defense of Human Body 15. Diversity of Generation of Imunoglobulin 16. A Magic Bullet (Monoclonal antibody) 17. Altered Response of Immune System 18. Compromise Between Immune System Cell, Organ and Tissue (Transplantation) 19. Effect of Aging on Immune Response 20. Restoration of Immune Function in Elderly Person