In these years of constant growth and further development for our company, research and development has become more and more important, and has allowed us to be at the forefront in our business sector, where innovation is the obvious and decisive factor. It has therefore been consistent with our everyday business philosophy to involve ourselves deeply in writing and printing this handbook, which is designed to recognize the capacity and hard work of all employees working successfully in the Bonfiglioli Group. The book is intended to be a concrete contribution by Bonfiglioli Riduttori S.p.A. to the development and application of power transmissions. The book is addressed to all who have technical dealings with power transmissions, from university students to engineers active in the workplace. For this reason we have invited the cooperation of four prestigious professionals - Darle W. Dudley, Jacques Sprengers, Dierk SchrOder, and Hajime Yamashina - in the knowledge that only through the cooperation of the leading specialists in the field of power transmissions could we develop a truly useful and helpful handbook. It has been hard work, but we are sure the reader's appreciation will amply reward our efforts.