The reactions of S-1 and D-3 Cu+ ions with N2O are studied by means of A initio methods. The structure of all stationary points along the reaction coordinate is optimized with density functional theory (DFT), using the B3LYP functional. The reaction and binding energies and the activation barriers are evaluated with DFT-B3LYP and also with the coupled cluster method CCSD(T). Three reaction paths were found, depending on the orientation of the approaching N2O molecule. If N2O approaches the Cu+ ions via its O-side, this leads to formation of CuO+ and N-2. On the other hand, if N2O attacks via its N-end, the reaction products are CuN2+ and an O atom. Finally, it was found that the D-3 Cu+ ions can also react with the central N of N2O, with formation of the insertion product [OCuN2](+). The most exothermic path is the insertion reaction of Cu+ into the N'(2)-O bond. The calculations indicate that bare S-1 Cu+ ions are relatively inert with respect to N2O: high energy barriers are calculated. The D-3 Cu+ ions, on the other hand, are strong activators of the N-2-O bond, and the reactions proceed without energy barrier, in agreement with experiment.