Membrane fouling is one of the major drawbacks for membrane-based technologies because it leads to severe flux decline which requires the fouled membrane to be cleaned and replaced on a regular basis. A systematic approach that is capable of providing early diagnosis is essential to control membrane fouling. Fouling index is a measure for fouling propensity of water in reverse osmosis applications. The present paper focuses on the review from the existing literature of the various fouling indices, i.e. SDI and MFI associated with a number of selected physicochemical factors. Despite of the fact that the membrane fouling problems and their forming mechanisms have been studied by numerous researchers, the evaluation on the contributing factors towards the fouling propensity is still remained unclear. Membrane fouling propensity can be influenced by: membrane morphology (i.e. surface porosity, membrane material, membrane hydrophobicity, membrane molecular cut-off, pore size), feedwater composition (i.e. ionic strength, pH, types and concentrations of feed), and hydrodynamic conditions (i.e. crossfiow velocity, permeate flux and temperature). These factors were discussed in great detail in the present review. (C) 2011 Elsevier B.V. All rights reserved.