In this paper, time-dependent results obtained from both a simple but nonlinear analytic similarity solution and a detailed numerical simulation model are used to study the interactions between the fundamental processes occurring in the ignition of homogeneous premixed gases. The parameters which may be varied are the composition of the mixture, the initial radius of energy deposition R o, the duration of the heating r 0, and the total energy deposited in the system E 0. The similarity solution plus the induction time for the fuel--oxidizer mixture as a function of temperature and pressure can be used to calculate whether a given energy source is adequate to ignite the system. This simple procedure is then calibrated using a time-dependent detailed numerical reactive flow model which includes the thermophysical properties of the mixture, a full chemical kinetics scheme, nonlinear convection, molecular diffusion, and thermal conduction. Calculations are presented for a selected mixture of H2-O2-N 2 for various values ofR 0 and E o. These show that the similarity solution predicts ignition accurately when the radius of energy deposition is larger than the quench radius. The detailed numerical reactive flow model is used to predict the quench radius and the absolute minimum ignition energy associated with it.