This book is intended as an introductory text for use in immunology courses for undergraduate and postgraduate students of Life Science and scientists in other fields who wants to know more about the basic concepts of immunology. It attempts to present the field of immunology from a consistent viewpoint. Hopefully this book will be a guide for teachers and students to understand the basic concepts of immunology. The author, deeply indebted to the Correspondent,the Principal and all the staff members of department of Microbiology and Biochemistry of M.I.E.T. Arts & Science college. Special thanks to my long standing friend for his support and encouragement throughout the work.