This paper is devoted to a review of microstructure observations performed on a TATB composition submitted to thermal and combined thermal/mechanical stimuli. Effects are identified and quantified in terms of decomposition extension and microstructure evolution (porosity, shear bands, grains shape and orientation, anisotropy...). Several complex mechanisms and important transformations are exhibited as a function of temperature, heating duration and shock wave intensity. Conclusions on decomposition mechanisms are directly derived from these observations.