HCCI/CAI has emerged as one of the most promising engine technologies with the potential to combine fuel efficiency and improved emissions performance. Despite the considerable advantages, its operational range is rather limited and controlling the combustion (timing of ignition and rate of energy release) is still an area of on-going research. However, commercial applications are close to reality. This book reviews the key international research on optimising its use, including gasoline HCCI/CAI engines; diesel HCCI engines; HCCI/CAI engines with alternative fuels; and advanced modelling and experimental techniques.