Development and diversification of machines and mechanisms with applications in all areas of scientific research requires new systematization and improvement of existing mechanical systems by creating new mechanisms adapted to the modern requirements; the gearing mechanisms are found today everywhere: in the industry of machinery construction, in energy industry, in aeronautics and aerospace, in electronics& Electrical, in oil industry, in mechatronics and robotics, etc. In this context this book attempts to bring a contribution to science and technology applied in the kinematic and dynamic analysis and synthesis of mechanisms with gearings. The book presents an original method to determine the efficiency of the gearing; the originality of this method relies on the eliminated friction modulus. With the relations presented in this paper, one can synthesize the gear's mechanisms; the best efficiency can be obtained with the internal gearing when the drive wheel 1 is the ring.