Some advantages to study intermolecular forces by IR overtone spectra are reported. The overtone intensity is nearly insensitive on interactions contrary to the large intensity increase of fundamental bands. As consequence H-bond equilibria and the structure of H-bonded liquids can be studied easier and in some directions with higher precision. Secondly, the simultaneous excitation of two H-bonded molecules by one quantum and this possibility to study H-bonds are shown. The determination of dipole moment changes by intermolecular interactions is described based on overtone spectra. Last but not least the possibilities to study van der Waals interactions in condensed media are given.