Cooling curve investigations show that the transition between the two crystalline forms of tetranitromethane occurs at -99.8°C and its character suggests an order-disorder transformation. The infrared spectra of tetranitromethane were obtained at 25°C (vapor), 18°C (liquid), -40°C (solid I), -88°C (solid I), -104°C (solid II) and -126°C (solid II). The spectra of the vapor are best interpreted by a molecule with S4-4̄ symmetry whereas reported Raman spectra indicate D2d-4̄2m symmetry in the liquid. Satisfactory agreement between these and the x-ray diffraction data require molecules of both symmetries. A complete lack of selection rules was observed in the spectra throughout the solid range.