Therapeutic antibodies are the fastest growing class of biopharmaceutical in development. They are highly specific for target recognition and accordingly produce highly selective results after their administration. This chapter will cover a brief history of monoclonal antibodies (mAbs), their types, classification, structures, mechanism of actions, and clinical uses. In addition, this chapter will demonstrate the uniqueness of mAb characteristics leading to mAbs use for abroad range of targets, such as cancer, autoimmune disease, gastrointestinal, rheumatologically, hematological, dermatological, metabolic, cardiovascular, central nervous system, ophthalmic, dental and infectious diseases. The dominant areas of mAb therapeutic application are in oncology, immunology, and hematology. Also, the recent potential role of mAbs to treat coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), will be reported.