The results of an extensive slow-neutron inelastic scattering study of heavy water at 299°K are reported. High-energy resolution measurements were made on thin D2O samples to obtain the double-differential scattering cross sections for energy transfers to 7 kT and momentum transfers to 9.5 Å−1. A spectral density for the modes of motion in D2O has been obtained by an extrapolation technique. Experimental results are presented in the form of the Egelstaff scattering function and are compared with calculations based on the McMurry-Russell modification of the Nelkin model for water and the Egelstaff-Schofield theory for an incoherent scatterer with a Gaussian self-correlation function.