The early applications of MF/UF relied on cartridge filtration to protect the membranes. The success of these stand-alone membrane installations has increased interest in MF/UF membranes from utilities with a wide variety of source waters. In order to treat challenging water supplies, additional processes must be considered for pretreatment before MF/UF, both to maintain the productivity of the membrane process and to meet treatment objectives that are not met by the membranes alone. To evaluate the impact of pretreatment and water quality on the membrane performance, this project was implemented with four major tasks: literature review, bench-, pilot-, and full-scale studies. The literature review covers conference proceedings and journal papers regarding the effects of pretreatment on membrane filtration. The primary focus of the bench-scale testing is to examine membrane fouling mechanisms by specific fractions of constituents in natural water. The effects of various pretreatment chemicals and pretreatment processes on each fraction were also assessed. Pilot testing is conducted on three different water sources using similar pretreatment conditions of the bench-scale study for providing the correlation among the different scales. The full-scale evaluation provides insight on operational and design issues that were impacted by membrane pretreatment The project findings provide guidance to water utilities for integrating MF/UF membrane process into existing or new water treatment plants. It is important to note, however, that results presented in this study may not apply to all cases and situations. Therefore, it is recommended that the overall conclusions be used to inform and guide utilities with the most cost-effective and suitable approach (i.e., bench-, or pilot-scale) to address specific concerns and optimize membrane performance.