Membrane Distillation (MD) is a thermally-driven separation process, in which only vapour molecules transfer through a microporous hydrophobic membrane. The driving force in the MD process is the vapour pressure difference induced by the temperature difference across the hydrophobic membrane. This process has various applications, such as desalination, wastewater treatment and in the food industry. This review addresses membrane characteristics, membrane-related heat and mass transfer concepts, fouling and the effects of operating condition. State of the art research results in these different areas will be presented and discussed. (C) 2011 Elsevier B.V. All rights reserved.