Offshore wind has been envisaged as making a critical contribution in Europe in satisfying the electricity demand in a low-carbon generation scenario. In fact, offshore environment provides a windier and steadier source compared to onshore wind energy. Offshore wind turbine rotors and generators create value by "farming" the wind, converting its energy into electricity. Costly infrastructure -- the very high towers, deep seabed foundations, buried high voltage insulated cables, on-platform transformers and complete subsea transmission grid -- and expensive at-sea maintenance are required because this electricity is not where it is needed. This book discusses offshore wind technologies and examines the ecological risks and prospects of offshore wind.