A theoretical study of the complexes formed between carbon monoxide, CO, and the hypohalous acids (HOX, X = F, Cl, Br, and 1) has been carried out using DFT [M05-2x/6-311++G(2d,2p)]and ab initio methods [(MP2/6-311++G(2d,2p) and MP2/aug-cc-pVTZ)]. Six minima were found, which correspond to two hydrogen-bonded complexes, two halogen-bonded complexes, and two van der Waals complexes. The hydrogen-bonded complexes with the carbon atom of the CO molecule are the most stable for hypohalous acids with X = F, Cl, and Br, whereas for X = 1, the halogen-bonded complex with the same atom of carbon monoxide is the most stable. A blue shift in the stretching frequency of the OH bond in the hydrogen-bonded complexes with the carbon atom of CO was observed. In addition, a blue shift was observed in the bond of the hypohalous acid not involved in the interaction.