Infrared spectra of aqueous solutions containing Ce(IV) and nitrate ions have been obtained by the attenuated total reflectance (a.t.r.) technique. Vibration frequencies and intensities have been measured and compared with infrared transmittance spectra and Raman spectra of both solutions and solids. The number of bands and the variation of band intensity with concentration changes indicate the presence of nitrato–cerium complexes in the solution. The polarization of the 1 538 cm−1 Raman band is advanced as a criterion that the coordination between the nitrate ion and the cerium(IV) ion is bidentate. Possible assignments are considered although many of the vibrations are characteristic of the ligand and hence are not diagnostic of a particular species.