Effective membrane pretreatment is a crucial requirement for trouble free and cost effective RO desalination Pretreatment construction costs are significant and may reach as much as 10%-20% of the total desalination plant capital costs This paper presents a general review of the central factors involved in assessing raw water quality The main foulant categories are described and the various unit operations commonly applied are reviewed Pretreatment aspects of desalination offer fertile grounds for advancing desalination technologies Promising research directions are highlighted (C) 2010 Elsevier BV All rights reserved