Biopharmaceuticals are large complicated molecules requiring researchers to apply sophisticated Design of Experiment (DoE) methods to optimize the multi-attribute reaction conditions for antibody or other protein conjugate Drug Substance Intermediates. The Design of Experiment (DoE) methodology accelerates understanding of the effect that process conditions have on the reaction and often leads to improved yield, lower consumption of expensive raw materials, and shorter development cycles. Applying Design of Experiment (DoE) in process development can serve as the basis of the Quality-by-Design approach, which is of increasing importance.