Wind turbine gearboxes are one of the major reliability problems for wind energy operators and cause expensive maintenance and repair jobs when failures occur, particularly in offshore wind farms. Gearless direct drive wind energy systems present a potential solution to these problems, improving both reliability and energy conversion efficiency through simplified design. The editors and contributors present a comprehensive reference on the design and operation of direct drive wind energy systems along with applications to direct drive marine renewable energy systems. The initial sections cover the fundamental design issues related to direct drive renewable energy devices, and their interconnection into transmission networks and review the impact on design of performance testing, monitoring and characterization techniques. Final sections cover the construction, operation and maintenance issues of direct drive wind and marine energy systems installation and look to the future developments and opportunities for application of this technology.