In this paper the historical perspective of the use of simulation in pulp and paper industry is presented and different applications discussed. Scientific papers as well as research and development work made by suppliers and software vendors is covered. The review covers a number of applications. First data reconciliation, root cause analysis and decision support is covered. This forms the basis for more advanced optimization and control. Physical models are then covered as they are especially good for engineering and design of new processes or the rebuilding of existing processes. As a complement for on-line applications quality property predictions with soft sensors like MVDA, ANN and grey box models are covered. When the process signals have been checked and soft sensors developed it is possible to perform process optimization and model based control and also to develop expert systems for decision support. Simulators also are used for operator training to increase the understanding of the processes as well as the interaction with the DCS system. Finally the future of process simulation in pulp and paper industry is discussed.