This proposal will explore the effect of elevated pressure on the widely used civil and military explosive TNT (trinitrotoluene). We are proposing a careful high-pressure neutron diffraction study on both polymorphs of TNT under hydrostatic conditions, with the aims of (i) identifying the evolution of structure as a function of pressure, including the changes in intermolecular interactions, (ii) exploring in detail the structural changes that occur near 2 GPa in the monoclinic form, (iii) exploring for the first time the effect of pressure on the orthorhombic form, and (iv) determining more reliable equations of state for the two polymorphs. These experimental results will be compared with the outputs from DFT-D calculations on each of the polymorphs as a function of pressure. These results will provide an enhanced understanding of the behaviour of this widely used material.