This short review is devoted to the description of the effect of the nature and the strength of intermolecular hydrogen bonds on structural properties of H-bonded complexes of aniline, phenol and pyridine derivatives. Several hundreds of such complexes, playing an important role in organic chemistry and biochemistry, have been identified and described in the literature. In the introductory part, the idea of the H-bond is discussed in terms of its historical development, followed by presently accepted classification of H-bonds. Critical review of quantum methods usually used for the calculations of the geometry of H-bonded complexes and the energies of H-bonds is then presented. In the second part, the H-bond-induced geometrical, hybridization and aromaticity index changes are discussed. All correlations based on quantum calculations are compared with those derived from the available crystal structure data. Although the experimental data are more scattered than the calculated ones, their agreement is impressive. This unequivocally shows the power of the calculation methods developed in recent years. Copyright © 2008 John Wiley & Sons, Ltd.