This chapter discusses the challenges in the scale-up of perfusion bioreactors from the few litres laboratory scale to the thousands of litres clinical and commercial scale. We consider comparative studies between laboratory- and large-scale reactor systems, including multiphase reactor models, computational fluidynamic tools as well as omics studies to support solid and reliable scale-up procedures. Specific scale-up issues – such as the scalability of the cell retention device, long-term operation, and batch definition in the case of process failure – are discussed. Finally, we evaluate the potential of single-use technologies and close the chapter with economic, financial, and environmental considerations in the context of future developments in biomanufacturing.