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The coordination structures of Cuii exchanged into ZSM-5 were obtained by B3LYP-DFT geometry optimizations on cluster models, representing the cation sites. The EPR g-factors of the resulting cluster models were calculated by means of the CASPT2 method multi-configurational perturbation theory, with the inclusion of spin–orbit coupling. In order to facilitate the confrontation of theoretical and experimental results, the EPR spectra of a selection of dehydrated Cuii-ZSM-5 samples are presented as well. The axially symmetric signal with g  2.30–2.33, which is present over the whole range of copper loadings, is assigned to a five-fold or distorted three-fold Cuii coordination in site α, a six-ring with bridging T-site, containing 2 lattice Al's. The axially symmetric species with g  2.26–2.28, present at medium copper loadings, is assigned to a square-planar Cuii coordination in six-rings and a square-pyramidal Cuii coordination in five-rings, with both rings containing only one Al and no extra-lattice oxygen ELO. The near absence of the g  2.26–2.28 signal at the highest Cu/Al ratio's is explained by the coordination of ELO to Cuii in these sites with one Al, yielding an EPR silent species.