Antibodies are Y-shaped protective proteins produced by the immune system in response to the presence of antigens. They consist of four polypeptides, including two heavy chains and two light chains. The Y-shaped structure allows the antibodies to perform two important functions, namely antigen binding and biological activity mediation. There are five different types of antibodies namely, IgG, IgM, IgA, IgE, and IgD. Immunoglobulin G (IgG) antibodies are large globular proteins consisting of two identical γ gamma heavy chains and two identical light chains. The function of IgG is to provide long-term protection against bacteria and viruses, and to neutralize bacterial toxins. The other function of IgG is to stimulate the complement protein systems and bind the antigens to improve the effectiveness of phagocytosis. The function of immunoglobulin A (IgA) antibodies is to bind the antigens on microbes before they can invade the tissues and emerge as a defense for mucosal surfaces, such as the intestines, nose, and lungs. This book aims to shed light on some of the unexplored aspects of immunology and the recent research in this field. It will provide comprehensive knowledge to the readers.