This proposal will explore the effects of elevated pressures and temperatures on the structures of two energetic co-crystals - [CL-20:TNT] and nitroguanidine:nitropyridone. CL-20, TNT, and nitroguanidine are used in explosive formulations and as propellants. The wider project aim is understand the types of structures formed by energetic co-crystals/salts, and discover whether these materials have enhanced properties, e.g. reduced sensitivity to accidental initiation, improved long-term storage and thermal stability. It is important to understand the responses of such materials to elevated pressures and temperatures, on the basis that extreme conditions are experienced during detonation processes. High-pressure structures inform us about how energy may be transferred within the material, thereby guiding the design of safer explosives and propellants.