The reactions of 3d transition metal atoms with N2O, producing the metal oxide and N-2, have been studied by means of density functional theory and the coupled cluster method CCSD(T). The importance of charge transfer in the reaction mechanism has been, investigated. For Sc, Ti, and V, the transition state is very reagent-like, and almost no charge transfer occurs. On the other hand, charge transfer from the metal 4s orbital into the N2O LUMO becomes more important when moving to the right in the 3d series. The reactions with Sc, Ti, and V proceed almost without energy barriers, whereas for Mn, Fe barriers around 9 kcal/mol are calculated. For transition metal atoms with a 3d(n)4s(2) ground-state configuration, a correlation is found between the activation barriers and the binding energy of the formed metal oxide. The 3d(n+1)4s(1) configuration gives rise to a higher reactivity than the 3d(n)4s(2) configuration.