The application of low pressure membranes (LPMs) to drinking water treatment and wastewater reuse has undergone accelerated development in the past decade. Integration of pretreatment with LPM filtration has been widely employed at full scale to reduce membrane fouling and/or increase the removal of certain aquatic contaminants. In principle, pretreatment of source water can impact membrane filtration in three ways: altering contaminant size distributions, changing mutual affinities of contaminants or their affinities to membrane surfaces, and suppressing undesirable microbial growth or removing biodegradable contaminants. The literature shows that, compared to the well-demonstrated enhancement of contaminant removal, impact of pretreatment to membrane fouling is often small or even negative, which isfurther complicated by variations in source water quality and membrane properties. Coagulation has been the most successful pretreatment for fouling reduction. Novel technologies are in immediate need for fouling control; ones which rely on a better understanding of the mechanisms of pretreatment and LPM filtration are warranted. This article provides a critical review of the state-of-the-art of pretreatment for LPMs, and discusses potential areas for future technical development and scientific studies.