Existing stop-start systems have several concerns such as take-off response, engine restart noise, high cost and system complexity. This paper describes a newly developed stop-start system that overcomes these concerns and can be used on high-volume production models at an affordable cost. The new system is based on a compact motor generator that allows cranking at restart and also functions as an alternator following engine start. A belt-driven system is used for restarting the engine to avoid noise from gear insertion and engagement.The motor generator is capable of high-speed operation for reducing engine startup time. Starting control has also been improved to achieve the shortest possible startup time in combination with a newly developed direct injection engine. Shortening the startup time tends to impair engine smoothness at restart. However, this concern has been resolved through cooperative control with the motor generator.The motor generator has approximately 1.4 times the electric generation capacity of an ordinary alternator of the same class. Together with improved battery charging performance, it achieves one of the highest levels of deceleration energy regeneration. A comparison of the regeneration capability under Japan's 10-15 test mode shows that this system has a large regeneration capacity of 120 kJ, compared with a maximum of 50 kJ for other systems. This means that electric power consumed during engine stop can be provided from the energy regenerated during deceleration, thereby achieving almost all fuel saving with the stop-start system.This paper describes technologies to improve the performance or countermeasures against the above concerns of a Stop-Start system. The new Nissan SERENA, which was launched in November 2010 in Japan, applies this start-stop system, compact motor generator, a newly developed direct injection gasoline engine and advanced starting control among the above technologies.