This book is on the electromechanical design aspects of a high-speed permanent-magnet synchronous machine integrated with a carbon fibre flywheel. The integrated machine is part of a flywheel energy storage system for use in a hybrid electric city bus. The book starts by investigating several energy storage technologies with the aim of finding the most suitable candidate for use in the energy storage system of a large hybrid electric road vehicle. High-speed composite flywheels emerge as the most suitable technology. The electrical machine design is approached analytically: a comprehensive analytical model of the electromechanics of the electrical machine is derived, based on 2D electromagnetic field calculations. The model includes the reaction field of the eddy currents in the shielding cylinder. The book advocates the use of analytical techniques in electrical machine design, arguing that it leads to quicker optimization of designs and greater insight into the problem.