This paper summarizes major design and operational issues of large scale microfiltration/ultrafiltration (MF/UF) projects. The world's largest are on the order of 100 mgd (378,000 m³/d). The discussion is highlighted by examples from two projects in Minneapolis with a combined capacity of 160 mgd (606,000 m³/d) and two in Singapore, 120 mgd (454,000 m³/d). In some ways, design and operational issues with world-scale MF/UF plants are similar to those for smaller facilities; however, even though the process is modular, well-engineered larger plants are not simply multiples of the smaller ones. Important issues include prevention of pressure surges and other hydraulic stresses, plant hydraulics, including the option of using gravity to optimize pumping costs; pilot programs; dynamic multi-train interaction; control philosophy; and special considerations at commissioning/start-up. A discussion of operations includes checklists of proactive maintenance tasks and troubleshooting to minimize the occurrence of problems and facilitate resolution. Includes tables.