Antibody conjugates are a diverse complex class of therapeutics, consisting of a potent cytotoxic agent linked covalently to an antibody or antibody fragment directed toward a specific cell surface target expressed by tumor cells or an extracellular target, that are having impact in the clinic. The notion that antibodies directed toward targets on the surface of malignant cells could be used for drug delivery is not new. The more than 30-year history of antibody conjugates is marked by hurdles that have been identified and overcome.Technology is continuing to evolve the protein and small molecule components, and it is likely that soon single-chemical entities will be the norm for antibody drug conjugates. More than 20 antibody conjugates are currently in clinical trials.The time has arrived for this technology to become a major contributor to improving treatment for cancer patients.