Wind turbine gearboxes present major reliability issues, leading to great interest in the current development of gearless direct-drive wind energy systems. Offering high reliability, high efficiency and low maintenance, developments in these direct-drive systems point the way to the next generation of wind power, and Electrical drives for direct drive renewable energy systems is an authoritative guide to their design, development and operation. Part one outlines electrical drive technology, beginning with an overview of electrical generators for direct drive systems. Principles of electrical design for permanent magnet generators are discussed, followed by electrical, thermal and structural generator design and systems integration. A review of power electronic converter technology and power electronic converter systems for direct drive renewable energy applications is then conducted. Part two then focuses on wind and marine applications, beginning with a commercial overview of wind turbine drive systems and an introduction to direct drive wave energy conversion systems. The commercial application of these technologies is investigated via case studies on the permanent magnet direct drive generator in the Zephyros wind turbine, and the Archimedes Wave Swing (AWS) direct drive wave energy pilot plant. Finally, the book concludes by exploring the application of high-temperature superconducting machines to direct drive renewable energy systems.