In situ XAFS combined with UV−vis−near-IR spectroscopy are used to identify the active site in copper-loaded ZSM-5 responsible for the catalytic decomposition of NO. Cu−ZSM-5 was probed with in situ XAFS (i) after O2 activation and (ii) while catalyzing the direct decomposition of NO into N2 and O2. A careful R-space fitting of the Cu K-edge EXAFS data is presented, including the use of different k-weightings and the analysis of the individual coordination shells. For the O2-activated overexchanged Cu−ZSM-5 sample a Cu···Cu contribution at 2.87 A with a coordination number of 1 is found. The corresponding UV−vis−near-IR spectrum is characterized by an intense absorption band at 22 700 cm-1 and a relatively weaker band at 30 000 cm-1, while no corresponding EPR signal is detected. Comparison of these data with the large databank of well-characterized copper centers in enzymes and synthetic model complexes leads to the identification of the bis(μ-oxo)dicopper core, i.e. [Cu2(μ-O)2]2+. After dehydration in H...