Monoclonal antibodies (mAbs) have demonstrated great therapeutic potential for the treatment of many conditions with over 100 therapies now approved for use The Antibody Society. Therapeutic monoclonal antibodies approved or in review in the EU or US. www.antibodysociety.org. Critically, a significant proportion of those approved target oncology, an area still in great need for breakthrough treatments. Although mAbs have demonstrated some therapeutic effectiveness in oncology, a mAb treatment may still lack sufficient antibody-dependent cellular cytotoxicity (ADCC) to be effective therapeutically. To overcome this inadequate ADCC activity and trigger a sufficient cell lysis response, the conjugation of cytotoxic small molecules to mAbs has been developed. These molecules, antibody drug conjugate (ADC) therapies, are now amongst the fastest growing drug classes in oncology with 11 approved for use in humans and the active development pipeline promises further products in future. This article describes in detail the important features of ADCs.