Complete vibrational assignments have been made for rhenium carbonyl and rhenium carbonyl iodide based upon their infrared and Raman spectra, and a force-constant calculation for the latter compound. The rhenium–rhenium stretching vibration is assigned to a Raman line near 105 cm.–1, and the rhenium-iodine stretching vibration to a Raman line near 165 cm.–1. The data is consistent with D4d and C4ν symmetry for the parent carbonyl and the carbonyl iodide, respectively.