Cubic cadmium(II) cyanide shows the most pronounced isotropic NTE effect known, with behaviour more than twice as extreme as that of better known materials such as ZrW2O8. Because NTE is driven by soft phonons, it is possible to gain important mechanistic insight from the structural response of Cd(CN)2 as a function of both temperature and pressure. This specific proposal aims to explore the GPa-range high-pressure behaviour of the compound. We will characterise any new phases that emerge at these higher pressures. The relationship of these phases to the ambient structure gives a direct indication of soft modes, and hence the mechanism for NTE.