In order to accurately control the ignition and fuelling of a gasoline engine, in the presence of environmental and system variability, it is necessary to measure the effect this variability has on the combustion process and then to initiate control action dependent upon this effect. Various systems have been proposed to gain a more comprehensive combustion measure than today's Lambda sensors can provide, including in-cylinder pressure, ionization probes, wide range exhaust gas oxygen sensors, etc. None of these systems has proven truly practical for volume production either because of the very high sensor cost, the computational load required by the signal processing, or performance limitations.This paper describes the application of in-cylinder optical probes to combustion feedback and control. The probes are used to measure the ignition delay and burn duration and these parameters are then maintained according to a mapped schedule by the concurrent control of ignition and fuelling. The prototype system is shown to exhibit good control over the production of NOx, being robust in the presence of system and environmental variability.In addition to the combustion timing control, the optical probes may be used to measure the level of cyclic variability and knock. The control of these variables can then be integrated into the principal combustion timing control scheme to provide a wide range of control through a single sensor.Two types of prototype combustion probe have been developed, one based upon a standard pressure sensor format, the other integrated into a spark plug.