Membrane fouling is a major problem in brackish and seawater desalination as well as in membrane mediated waste water reclamation. Fouling of nanofiltration (NF) membranes is typically caused by inorganic and organic materials present in water that adhere to the surface and pores of the membrane and results in deterioration of performance (reduced membrane flux) with a consequent increase in costs of energy and early membrane replacement. Natural organic matter (NOM) fouling of NF membranes involves interrelationship between physical and chemical interactions and it is described in this review. Membrane fouling in the presence of NOM can be influenced by: membrane characteristics, including surface structure as well as surface chemical properties, chemistry of feed solution including ionic strength, pH and concentration of monovalent ions and divalent ions, NOM properties, including molecular weight and polarity, and hydrodynamic and operating conditions including permeate flux, pressure, concentration polarization, and the mass transfer properties of the fluid boundary layer. These factors will be discussed in details in this review. Inorganic fouling due to scale formation of sparingly soluble inorganic salts occurs whenever the ionic salt concentration stream exceeds the equilibrium solubility. Scale formation take place by homogenous or heterogeneous crystallization and its factors will be also investigated in this review. (C) 2010 Elsevier B.V. All rights reserved.