The spatial networks of hydrogen bonds in liquids and solutions are defined and described through a series of diols, aminoalcohols and diamines, and their comparison with the spatial network of water is explored. The authors review the structural and energetic features of classical hydrogen bonds in order to emphasize the most important aspects for rationally designing crystalline and molecular materials. Lastly, the formation of intra- and intermolecular hydrogen bonds in recently synthesized hetarylmethylidene cycloalkanones and their influence on the stabilization of otherwise unstable isomers and tautomers is considered on the basis of experimental and theoretical analyses.