Friction stir welding is a relatively new joining process developed initially for aluminum alloys. It is a solid-state joining technique that is energy efficient, environment friendly, and versatile. This book covers the rapidly growing area of friction stir welding. It also addresses the use of the technology for other types of materials processing, including superplastic forming, casting modification, and surface treatments. The book has been prepared to serve as the first general reference on friction stir technology. Information is provided on tools, machines, process modeling, material flow, microstructural development and properties. Materials addressed include aluminum alloys, titanium alloys, steels, nickel base alloys, and copper alloys. The chapters have been written by the leading experts in this field, representing leading industrial companies and university and government research institutions.