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.