Part of the UK's National Energy and Climate Plan is to seek, in cooperation with the EU to support the delivery of cost-effective, clean, and secure supplies of energy with a large part of this is to come from harnessing offshore wind in the North Sea. The European Commission has estimated that offshore wind from the North Seas can cover up to 12% of the electric power consumption in the EU by 2030. To do this offshore wind turbines are having to be built to operate in deeper waters and further offshore which allows for higher and more consistent wind loads as well as greater public acceptance due to lower visual and environmental impacts that otherwise accompany offshore wind turbines. However, as this happens it becomes increasingly economically viable to mount the wind turbine on a floating structure which is tethered to the sea floor rather than conventional methods of using a concrete anchor or driven monopoles. But the wind industry is facing many challenges on the design, manufacturing, installation, operation and maintenance of floating offshore wind turbines (FOWT), and among which the most critical challenge is the reliable methodology for predicting nonlinear dynamic responses of FOWT under complicated sea states. The FOWT is a typical rigid-flexible multi-body system, as such it must not only remain buoyant but also limit responses in pitch, roll and heave as well as maintaining position in a large variety of conditions. Excessive responses can lead to higher structural stresses and as such would incur higher costs to make the system structurally sound compared to a system encountering smaller responses, the efficiency of the turbine is also reduced by large rotational responses in pitch and roll which would also add additional wearing onto the turbine components increasing the need for repair and maintenance. As such being able to predict the responses of a FOWT system due to the multiple loads it is put under and reduce them would be required for cost-effective, efficient, and safe designs. The aim of this project is to improve the accuracy of dynamic response prediction of FOWTs and to develop a numerical programme to solve the aero-hydro-elastic-mooring-servo coupled equations of a FOWT. This project is undertaken in partnership between Newcastle University, the ReNU Centre for Doctoral Training, and the Offshore Renewable Energy Catapult. This aero-hydro-elastic-mooring-servo numerical programme will consider the loads from aerodynamics, hydrodynamics, and mooring lines acting on the FOWT in various conditions, this will be coupled with structural and multi-body dynamics in order to predict the response of the FOWT in various sea states. Furthermore, control theory will be applied to discern methods of damping and reducing the responses of the FOWT using control systems. It will allow designers to consider different floating body concepts and which concept of floating body would be suitable for the area of operation that the FOWT will be placed in. The programme will be applied for code-to-code comparison with other codes as well as with published basin experimental data or full-scale measured data. It will also be applied in industry practice with a 7MW FOWT with the support of the Offshore Renewable Energy Catapult.