Wave, tidal and offshore wind technologies have long held the promise of seemingly limitless energy supplies. In practice, while offshore wind is growing relatively rapidly, all three sectors have lagged behind expectations. This book, from the International Energy Authority Renewable Energy Technology Deployment implementing agreement (IEA-RETD), examines the reasons for this and suggests how barriers to deployment might be overcome. Beginning with an assessment of the marine energy resource, it provides a detailed introduction to the main technologies currently being employed to harness wind, tidal and offshore wind power. It then examines the types of policies which are used to encourage deployment around the world, and progress towards meeting targets. The economics of offshore energy projects are discussed, along with risks that projects face and the types of finance which are available. A final section turns to barriers - both technical and non-technical (including environmental, health and safety, skill related, supply chain and more) - and in all cases suggests how to mitigate and remove these barriers. Highly illustrated in full colour, this is an indispensable resource for anyone - whether in industry, policy or academia - looking to learn more about how deployment of offshore renewable energy technologies can be encouraged.