Monoclonal antibodies have been considered promising therapeutic entities due to their highly specific binding to antigens. For oncology in particular, the tumor specific binding of an antibody, without affecting normal tissue, is considered an ideal cancer therapy. Although the proposed mechanism of action of antibody therapeutics varies by targets and indications, antibody-dependent cytotoxicity (ADCC), complement-dependent cytotoxicity (CDC), ligand neutralization and inhibition of the signaling pathway are commonly used. Recent advances in genomic information, genetic engineering, and transgenic technology have greatly accelerated drug development processes. It is also possible to add new functions to antibody molecules through molecular engineering. For example, antibody-drug conjugates (ADC), which combine a monoclonal antibody and a small-molecule cytotoxic drug, have been successfully used for cancer treatment. It has been more than 20 years since the first therapeutic antibody was approved in Japan, and there are now more than 30 antibodies on the market, with many new molecules under development. Despite some drawbacks and challenges, antibody therapeutics hold great promise as we advance our knowledge and technologies in the coming years.