Immunoglobulin G (IgG), one of the most abundant antibodies in the human body, has a molecular mass of approximately 160 kDa, which is due to the presence of two light chains and two heavy chains. The Fab region present within the IgG structure contains a paratope and can help in pathogen inhibition through recognition events, while the Fc region is responsible for interacting with different accessory molecules to regulate indirect effector operations. These operations include the complement-dependent cytotoxicity mechanism (CDC), antibody-dependent cellular cytotoxicity, and phagocytosis (ADCC and ADCP). The structure of IgG subtypes and allotypes has been extensively studied for more than a half century, and the differences have been illustrated in other literatures, with the different regions and various components of IgG. Schematics for the structure of other immunoglobins such as IgE, IgD, IgA, and IgM have also been provided in literature. This detailed understanding of the structure of immunoglobulins has led to the development of therapies such as monoclonal antibodies, which target specific antigens and have shown promising results in the treatment of various diseases. The human immune system is a complex network of cells, tissues, and molecules that work together to defend against foreign invaders such as bacteria, viruses, and parasites. Based on the type of molecules involved in providing the defense mechanism, human immunity can be categorized into two types, cell-mediated immunity and humoral immunity. Cell-mediated immunity involves the role of T cells, which directly attack infected cells, while humoral immunity works through the use of antibodies. Antibodies, also known as immunoglobulins, are small proteins produced by the immune system that bind to foreign substances known as antigens, and play a crucial role in defending against infections. Of all the immunoglobins present in the plasma, IgG is an important class of antibodies that constitutes 75% of them, and plays a key role in humoral immunity. IgG has the ability to bind with a diverse number of molecules due to the primary amino acid sequences, which diversifies its capability to tackle pathogens. The defense mechanism of IgG against pathogens is complex and involves multiple mechanisms, including neutralization of toxins, opsonization, and complement activation. Neutralization of toxins involves the ability of IgG to bind to toxins and render them harmless, while opsonization involves the coating of pathogens with IgG, which then facilitates their recognition and phagocytosis by immune cells. Complement activation involves the binding of IgG to pathogens, which then triggers the activation of the complement system, leading to the destruction of the pathogen. These mechanisms show the different ways in which IgG interacts with pathogens to protect the host. In addition to its role in defending against infections, IgG also plays a vital role in various other physiological processes such as placental transport, immune complex formation, and inflammation. The high abundance of IgG in plasma and its diverse mechanisms of action have made it an important target for diagnostics and therapeutics. IgG-based serological tests have become important biomarker tools for diagnosing and monitoring infectious diseases such as COVID-19, and the therapeutic potential of IgG has been demonstrated in various diseases such as autoimmune disorders and cancer. The importance of IgG in improving immunity, treating pathological diseases, and serving as a biomarker, as well as its role in vaccines and biosensors for diagnostics, underscores its critical role in human health.