iGVPT2 is a program for computing anharmonic corrections to vibration frequencies, based on force field expansion of the potential energy surface in normal mode coordinates. It includes second order vibrational perturbation theory (VPT2) algorithm and its derived methods (VPT2+K, DCPT2, HDCPT2). iGVPT2 is interfaced with several computation chemistry packages to compute the potential energies and dipoles derivatives. The second, third and quartic derivatives can be computed at the same level of theory but they can be also computed using different methods via one or two computational packages. iGPVT2 includes also a very fast hybrid QM//MM approach for biomolecules. It is provided free-of-charge for non-commercial research (see \url{https://sites.google.com/site/allouchear/igvpt2}).