The structure and energetics of the complexes formed between H2O and CO have been investigated by FTIR matrix isolation spectroscopy and ab initio molecular orbital theory. Two stable minima were found representing nearly linear hydrogen bonds between the subunits. The H2O-CO and H2O-OC species were calculated to be bound by 6.89 and 2.35 kJ mol(-1), respectively, at the MP2/6-311++G(2d,2p) level of theory. The computational results were reproduced by experimental assignments for both type of complexes in low-temperature argon, krypton, and xenon matrices. The CO fundamental mode was observed to shift to higher wavenumbers from its monomer value as the CO subunit was attached from the carbon end. instead, for the H2O-OC complex the nu(CO) shifts to lower wavenumbers. The water stretching and bending fundamentals were considerably perturbed upon complexation. Annealing processes were performed, and the dynamics of the complex species have been discussed.