We perform a joint experimental–theoretical study of the electrochemical oxidation of CO on copper (Cu) under alkaline conditions. Using cyclic voltammetry on Cu single-crystal surfaces, we demonstrate that both Cu terraces and steps show CO oxidation activity at potentials just slightly positive (0.03–0.14 V) of the thermodynamic equilibrium potential. The overpotentials are 0.23–0.12 V lower than that of gold (≈0.26 V), which until now has been considered to be the most active catalyst for this process. Our theoretical calculations suggest that Cu’s activity arises from the advantageous combination of simultaneous *CO and *OH adsorption under CO oxidation potentials and surmountable *CO–*OH coupling barriers. Experimentally observed onset potentials are in agreement with the computed onsets of *OH adsorption. We furthermore show that the onsets of *OH adsorption on steps are more affected by *CO–*OH interactions than on terraces due to a stronger competitive adsorption. Overall, Cu(100) shows the lowest overpotential (0.03 V) of the facets considered.