Sourcing for the manufacture and control of Antibody-Drug Conjugates (ADCs) used in clinical trials requires strategic planning, establishment of a specialized support network, and execution of several interdependent tasks. ADCs are complex molecules, a fusion of a biological, the monoclonal antibody (mAb), and of small molecules, the linker and the toxic payload. Facilities of acceptable standards for the handling of high potency materials need to be engaged, and there is a limited supply currently. This is further complicated by the fact that there is not one contract facility that has fully integrated services, a “one-stop shop” capable of mAb production, linker and/or payload synthesis, conjugation of mAb to linker-payload to make the Drug Substance, and finally, formulation of the ADC to make the Drug Product. Strategizing the best outsourcing practices for producing and testing ADCs, and establishing guiding principles for externalization to ensure the selection of the right CMOs for ADC outsourcing and technology transfer, will be further discussed.