MP2/6-311++G(-+) calculations were performed on HF...H2O, HF...NH3, HF...LiH, (H2O)(2), (HCOOH)(2), C2H2...H2O, H2O...NH3, (C2H2)(2) complexes to characterise different hydrogen bonds: typical as O-H...O and O-H...N, weak like C-H...O and C-H...pi, dihydrogen bonds, etc. For such heterogeneous samples a new measure of hydrogen bond strength was introduced. The Bader theory was also applied to characterise hydrogen bonds.