In coastal and offshore engineering, complex, generally highly nonlinear and distorted, wavemotion, which may involve breaking, bore propagation, aeration, structure interaction and violent impact, has remained largely intractable to numerical modelling. Smoothed particle hydrodynamics (SPH) holds great promise since it solves the governing equations in Lagrangian form where each particle represents an interpolation of local fluid quantities that carry flow quantities such as mass, pressure, velocity and move according to their underlying mechanics. SPH is thus a meshless method and possesses some unique advantages over conventional mesh-based approaches; no explicit treatment of the free surface and no computational grid mean that sophisticated meshing is not needed for complex fluid or solid geometries. The method is advancing rapidly, both in fundamental development and in its range of applications. An SPH approach has been developed which is truly incompressible, accurate and virtually noise free but, until recently, numerical instability has been a difficulty. This has been solved by a recent development at Manchester which maintains accuracy, efficiency and relative simplicity. The noise-free aspect is important for fluid/structure interaction since noisy pressures would contaminate forces. The effects of trapped air on impact pressures is also known to be important and surface tension determines the nature of wave breaking. These two effects may be incorporated in SPH. The aim of this project is to make the ISPH method into an attractive engineering tool, with the code able to handle very large numbers of particles, particularly in 3-D, using parallel computing to enable a wide range of applications. This would be undertaken at three levels as: a single-phase incompressible, almost inviscid flow solver; a two-phase water/air solver, with air compressible; a two-phase water/air solver with surface tensionTo this end a 3-D numerical coastal wave basin will be developed with the option of including structures of arbitrary geometry such as sea walls, caissons, wind turbine columns, harbours, ships.