Tetrathiafulvalene (TTF) is a key molecule in the family of charge-transfer salts of interest for their novel transport properties. The correspondence between transport property and electron-molecular vibration coupling requires that we understand the phonon density of states for these materials. Here we report the results of a low temperature study of neutral TTF using both inelastic neutron scattering spectroscopy and Raman spectroscopy. The new data has been interpreted using the CLIMAX code to calculate the neutron spectral profile which has also been calculated based on a set of force constants derived using Density Functional Theory to calculate the ground state energy of neutral TTF. The two approaches lead to a concordant set of harmonic force constants for the in-plane and out-of-plane normal modes of TTF.