Geometrical data on hydrogen bonds to halide ions are compiled from the currently available crystal structures. Hydrogen bonds from 25 donor types tō uoride, chloride, bromide and iodide ions are considered. Compared with earlier compilations, the increased data volume allows a ®ner subdivision of OÐH and NÐH donors, and the donors CÐH, SÐH and PÐH can be included. For a given donor type, the hydrogen-bond distance typically increases by over 0.5 A Ê from¯uoride to chloride, 0.15 A Ê from chloride to bromide and 0.25 A Ê from bromide to iodide acceptors. The strongest of the CÐH donors considered, chloroform, forms hydrogen bonds with chloride ions with an average HÁ Á ÁCl separation of only 2.39 A Ê and an average CÁ Á ÁCl separation of 3.42 A Ê . The lengthening of the NÐH covalent bond in hydrogen bonds to chloride ions is quanti®ed from neutron diffraction data.