The branch of biology which focuses on the immune system of various organisms is termed as immunology. It involves the process of charting, measuring and contextualizing the physiological functioning of the immune system in states of both health and disease. The chemical, physical, and physiological characteristics of the components of the immune system are also studied under it. The discipline of immunology can be broadly categorized into classical immunology, clinical immunology and developmental immunology. It finds applications in numerous branches of medicine, especially in the domains of organ transplantation, oncology, rheumatology, virology, bacteriology and psychiatry. Immunotherapy is defined as the use of antigens and other immune system components to treat a disease or genetic disorder. In order to achieve the desired therapeutic goal, modern immunology has become increasingly selective in its manipulation of the body's immune system. This book is a valuable compilation of topics, ranging from the basic to the most complex theories and principles in the field of immunology. While understanding the long-term perspectives of the topics, it makes an effort in highlighting their impact as a modern tool for the growth of the discipline. This book attempts to assist those with a goal of delving into the field of immunology.