A new model of ignition delay is formulated and the equations which govern ignition are presented. The model is based on fuel molecules having discrete allowed energy levels, and interprets radicals simply as additional allowed energy levels. Using such a model, the initial fuel temperature can readily be accounted for and its effect on ignition delay predicted. Equations for the general multilevel system are presented, as is the detailed solution for the simple two-level system. Theoretical results predict that the ignition delay can be made arbitrarily small and essentially independent of air temperature if the fuel is sufficiently preheated.