Exposure to X-ray and gamma-ray radiation profoundly alters the thermal stability and decomposition characteristics of ammonium perchlorate in the solid state. The radiation-induced changes in chemical reactivity were revealed by investigations involving thermogravimetric experiments and differential thermal analysis, where temperature is increased continuously at a constant rate, isothermal rate studies as a function of temperature, hot stage microscopic and X-ray diffraction studies, and electron spin resonance. This paper presents both a review and evaluation of recent investigations and new experimental results and interpretations of the reaction mechanisms.