We have presented the first analytic calculations of anharmonic corrections to both the vibrational frequencies and intensities in infrared and Raman spectroscopies. This has been made possible by our recent development of a recursive scheme for the calculation of high-order molecular properties, including properties involving frequency-dependent perturbations and perturbation dependence in the basis set.47 The approach is applicable to single-determinant self-consistent field models such as Hartree–Fock theory and Kohn–Sham DFT, and being matrix-based, it can also be extended to linear-scaling approaches,48,62 as well as to the relativistic four-component level of theory.86 We have previously applied our approach to the calculation of anharmonic corrections to vibrational frequencies using density functional theory46 and to the analytic calculation of Raman optical activity87 and hyper-Raman scattering,71 and in this work, we have used it to calculate anharmonic infrared and Raman spectra of nitromethane and its partially deuterated isotopomers. We find that anharmonic effects lead to an improvement in the quality of the computed IR and Raman spectra. The major improvements arising from the anharmonic treatment occur for the vibrational frequencies, while the effects of the anharmonic corrections on the infrared and Raman intensities are smaller and show only minor influences on the relative intensities of the fundamental bands, which is in agreement with earlier observations.38 Nevertheless, the anharmonic corrections are important in order to capture the overtone and combination bands. The anharmonic corrections are found to be somewhat more important for the Raman spectra, even if very small, than for the infrared spectra. Overall, the anharmonic spectra are in better agreement with experiment than the corresponding harmonic spectra.