The development of offshore wind power has become a pressing energy issue, driven by the need to find new electrical power sources and to reduce the use of fossil fuels. Offshore wind farms can harness tremendous wind resources without annoying citizens and with a comparatively low environmental impact. They are thus becoming a central pillar of a carbon free energy system. However offshore turbines and wind farms are costly to install and maintain, making reliability and cost-effectiveness key issues. This work covers reliability of offshore wind farms as a whole, starting from weather and wind conditions, dealing with wind turbine technology, farm layout, monitoring, safety and maintenance. The thoroughly revised second edition additionally covers turbines of up to 10 MW, turbine design changes, turbine converters, HVDC converter stations and DC links, offshore sub-sea collector and export cables, and the structures supporting large offshore wind farms.