The Book describes theories and modeling of Permanent Magnet based GOPI engine in details. The main focuses of the work is to explaining the Design and Development of fuel less technology/ device to replace or in substitute of Fuel based devices. The GOPI Engine uses permanent magnetic repulsive force to produce thrust. It is well known that the permanent magnets have magnetic free energy associated with them but there is no device available to make a direct use of it. In the development of the GOPI engine, this magnetic free energy is converted into magnetic potential energy and then into magnetic kinetic energy. This magnetic kinetic energy is then used to operate the engine.