Large-scale industrial downstream processes of biotechnological products have utilized ultrafiltration/diafiltration processes since the mid-1970s, when conven­ tional separation techniques, such as salt precipitation, centrifugation, evapora­ tion, lyophilization, and membrane dialysis were supplemented/replaced with al­ ternative industrial-grade ultrafiltration membranes. Two primary objectives have been addressed: concentration of biological products from dilute solutions (ultra­ filtration), and removal of small molecules via constant-volume buffer exchange (diafiltration). The availability of membranes in the molecular-weight cutoff range of 500 to 1,000,000 Daltons (Da) and manufactured with a wide range of polymers provides a reasonable degree of choice to the process engineer. Indus­ trial-grade ultrafiltration membranes are amenable to cleaning in place for reuse, the process of which is extensively validated.