Molecular dynamics simulations are used to calculate the incoherent neutron scattering spectra of myoglobin between 80 K and 325 K and compared with experimental data. There is good agreement over the entire temperature range for the elastic, quasi-elastic, and inelastic components of the scattering. This provides support for the accuracy of the simulations of the internal motions that make the dominant contributions to the atomic displacements on a time scale of 0.3-100 ps (100-0.3 cm-1). Analysis of the simulations shows that at low temperatures a harmonic description of the molecule is appropriate and that the molecule is trapped in localized regions of conformational space. At higher temperatures the scattering arises from a combination of vibrations within wells (substates) and transitions between them; the latter contribute to the quasi-elastic scattering.