A theoretical model is presented for the X-H/X-D stretching vibrations in weak and moderately strong hydrogen-bonded systems. The model is based on vibronic-type couplings between high and low frequency modes in hydrogen bridges and Davydov interactions- It allows calculation of energy and intensity distributions in the infrared spectra of hydrogen-bonded systems. The effect of deuterium/hydrogen substitution on the spectra and the temperature effect are explained. Comparison between experimental and theoretical spectra is presented for several systems with hydrogen bonds, crystalline, liquid and gaseous. (C) 2004 Elsevier B.V. All rights reserved.