Many different types of wave energy converters have been proposed in recent years. The two primary de- sign considerations are the need to generate energy at competitive economic rates in average sea states and the need for the wave energy converters (WEC) to survive extreme wave conditions. Due to the complexity of most offshore wave energy devices and their motion response in different sea states, model scale tank tests are common practice for WEC design. Full scale tests are also neces- sary, but are expensive and only considered once the de- sign has been optimised. Computational Fluid Dynamics (CFD) is now recognised as an important complement to traditional physical testing techniques in offshore engi- neering. Once properly calibrated and validated to the problem, CFD offers a high density of test data and results in a reasonable timescale to assist with design changes and improvements to the device. This paper deals with the results of test cases leading towards sim- ulation of the full dynamics of Pelamis and the Manch- ester Bobber. The test cases presented involve the inter- action between waves and fixed horizontal cylinders and results are compared with experimental data to validate the CFD codes. Also results for fluid-structure interac- tion of an oscillating cone on the water surface are pre- sented. The surface elevation and diffraction effects are discussed, as well as the forces on the structures due to the waves and motion respectively. Four different CFD codes are applied to simulate the test cases: Smooth Par- ticle Hydrodynamics, a Cartesian Cut Cell method based on an artificial compressibility method with shock cap- turing for the interface, and two pressure-based Navier- Stokes codes, one using a Finite Volume and the other a control volume based Finite Element approach.