The chemical deactivation of Cu-SSZ-13 Ammonia Selective Catalytic Reduction (NH3-SCR) catalysts by Pt, Zn, Ca and P has been systematically investigated using a range of analytical techniques in order to study the influence on both the zeolitic framework and the active Cu2+ ions. The results obtained demonstrate a crucial impact of P, completely suppressing the catalytic activity as a result of different deactivation mechanisms (i.e. site blocking, disruption of the zeolite framework, CuO formation and else reduction in the number of isolated Cu2+ ions). A less pronounced drop in activity is found with Ca and Zn introduction, without an appreciable adverse effect on N2 selectivity, since the catalytic deactivation is mainly brought about through a pore blocking/filling mechanism. Additionally, a drop in the amount of Cu2+ ions with the formation of CuO species also takes place, observed to be most important for the Zn-deactivated materials. Deactivation by Pt strongly affects N2 selectivity, but without a significant influence on the active sites or the zeolitic structure, basically due to the high oxidation activity of the Pt species, which highly promote N2O and NO2 formation.