Ignition characteristics of representative composite solid propellants were studied using an arc-imaging furnace to provide a radiant energy source. The variation of propellant ignitability with formulation changes was found to be small provided the binder and oxidizer were fixed. The minimum initial pressure for which ignition will occur appears to be predominantly determined by the thermal decomposition characteristics of the binder component in ammonium perchlorate-based propellants. It is proposed that a key step required to achieve ignition is the establishment of a critical gas-phase reaction rate threshold adjacent to the propellant surface.