To reduce the time and cost of developing an engine, a unified design approach would be interesting. In this context, control and development of internal combustion engines could also be unified. Obviously, this control must be stable, robust with respect to manufacturing disparities and operating points. This book then focuses on a unified approach for gasoline engines as well as diesel engines, to achieve a robust of the air-path. The engine air path contains the information needed to control the amount and proportions of air and neutral gases in the cylinder(exhaust gas recirculation, throttle valve, turbocharger). This unified approach to control monovariable systems, as well as non-square multivariable systems (number of inputs different from the number of outputs). The coupling inputs to outputs and onlinearities are taken into account during the synthesis of the controller. This design method has been validated in several applications including a gasoline engine and a diesel engine.