CuZSM-5 is the most active catalyst known for the direct decomposition of NOx. We have performed first-principles quantum mechanical calculations to evaluate the electronic and structural properties of species adsorbed to Cu sites that might be involved in NOx decomposition, Using statistical mechanics, we have calculated Delta U degrees, Delta H degrees, and Delta G degrees of possible elementary reactions in order to evaluate the stability of adsorbates on Cu sites and the ease of their interconversion. On the basis of these calculations, we propose a reaction pathway for NOx decomposition. This scheme involves only single, isolated copper sites, is internally consistent, and is consistent with experimental observations.