Abstract The chemisorption of CO on Cu(111) in the temperature range 7–77 K has been investigated with infrared reflection absorption spectroscopy and LEED. Initial adsorption at 7 and 77 K is characterised by the appearance of a linear CO species ( ν( CO) = 2078−2070 cm −1). Adsorption to higher coverages at 77 K, when the CO overlayer produces a hexagonal LEED pattern, gives rise to additional infrared bands at frequencies associated with bridging species (ν(CO) = 1830 and 1812 cm −). The same overlayer of CO at 7 K exhibits only one of the two bridging CO bands ( ν ( CO) = 1830 cm −1) as well as the linear band. The temperature dependence of the bands in the bridging region is explained in the same way as similar observations for CO adsorption on Pt(111). Experiments at these low temperatures have also enabled us to study physisorbed CO ( ν( CO) = 2141−2138 cm −1) with infrared spectroscopy. Even at 7 K the physisorbed species does not adsorb on the bare surface: almost saturation coverage of the chemisorbed species is required.