The chemical processes involved in the decomposition and combustion of energetic materials have been investigated theoretically using quantum chemical methods to determine the thermochemistry and reaction pathways. The Bond-Additivity-Corrected Moller-Plesset fourth-order perturbation theory method (BAC-MP4) has been used to determine heats of formation and free energies of reaction intermediates of decomposition and combustion. In addition, the BAC-MP4 method has been used to determine reaction pathways involving these intermediates. A theoretical method for calculating solvation energies has been developed to treat the non-idealities of high pressure and the condensed phase. The resulting chemical processes involving decomposition, ignition and combustion are presented for nitramines and nitromethane. Differences in decomposition mechanisms for the condensed phase and gas phase are discussed. In addition, we discuss the effects that amines can have on the initial stages of condensed-phase nitromethane decomposition. Bond dissociation energies for nitro-triazoles are compared with those of other nitro compounds.