The offshore wind industry has experienced significant growth in recent years, and continues to expand both in the UK and worldwide. Most of the offshore wind turbines installed to date are located in relatively shallow water and are mounted on fixed bottom support structures. Given the limitation of suitable shallow water sites available with high wind resources and also to reduce the environmental and visual impact of turbines, it is necessary to extend wind turbines to deeper water through the development of floating offshore wind turbine (FOWT) systems, which mount wind turbines on floating support platforms. The project aims to fill an important gap in the design, manufacturing and testing of emerging FOWT techniques by specifically characterising extreme loading on FOWTs under complex and harsh marine environments. These are typically represented by storm conditions consisting of strong wind, extreme waves, significant current, rising sea level and complex interplay between these elements, through a coordinated campaign of both advanced CFD modelling and physical wave tank tests. This has direct relevance to the current and planned activities in the UK to develop this new technology in offshore wind. In addition, the project aims to develop a suite of hierarchical numerical models that can be applied routinely for both fast and detailed analysis of the specific flow problem of environmental (wind, wave, current) loading and dynamic responses of FOWTs under realistic storm conditions. As an integral part of the project, a new experimental programme will be devised and conducted in the COAST laboratory at the University of Plymouth, providing improved understanding of the underlying physics and for validating the numerical models. Towards the end of the project, fully documented CFD software and experimental data sets will be released to relevant industrial users and into the Public Domain, so that they may be used to aid the design of future support structures of FOWTs and to secure their survivability with an extended envelope of safe operation for maximum power output.