ZrW2O8 is the classic example of a material exhibiting negative thermal expansion (NTE), i.e. lattice shrinkage on warming. The origin of this behaviour has been controversial for a long time, but is widely believed to be intimately linked to the lattice dynamics. Recent ab-inito studies have suggested that there is no single phonon mode that is responsible for the NTE, rather a collection of low energy modes all contribute. These same ab-initio studies have been used to explain the origin of negative hydration expansion (lattice shrinkage on intercalation of water) in ZrW2O8. The aim of this proposal is to verify the calculations directly using single crystal inelastic neutron scattering to measure how all of the low energy modes shift as a function of temperature, a key prediction of the theoretical work.