The validation of the “interFoam” CFD model (part of the OpenFOAM) CFD library is described for a number of wave/structure interaction problems. The background to the research is described, including the reasons for the selection of a new, previously unvalidated CFD code for this purpose. The numerical aspects of the code are briefly reviewed as are some of its additional features including the simulation of porous media. The new wave-generating boundary condition, created as part of this project, is described. The model is validated for the propagation of waves, including violent, breaking waves, using the widely-known “Dingemans” test case as well as new data for wave and focussed wave group propagation over a bar. The model is validated for wave interaction with surface-piercing structures by examining a test case for focussed wave-group impact on a surface-piercing cylinder with one near-breaking wave and a second, breaking, wave. The model is shown to perform well in these cases without the need for calibration and can therefore be considered to be a valuable design tool. It is also shown that in these cases the model can run sufficiently fast to be practical and economic for use as a design tool. The model is validated for porous media with a case examining porepressure transmission through a porous breakwater. The model performs poorly without calibration, highlighting the high levels of uncertainty in the Darcy parameter, but once calibrated is found to produce accurate results in very reasonable time. A case study of a porous roundhead defence structure is also presented to further reinforce the practical usefulness of the model in design.