Practical application of models developed by the research community to predict the performance in low-pressure membrane process is very limited. Several factors are responsible for the current gap between research and practice. First, a solid understanding of fouling mechanisms has not been achieved. Second, current knowledge of existing process models has not been consolidated into a single publication for the practice community. And third, practical examples of the successful use of models are still lacking. Fouling mechanisms and process models are brought together in this review with the aim of presenting a unified conceptual framework and demonstrating some important practical implications for process design and operation. (C) 2009 Elsevier B.V. All rights reserved.