Dynamic nuclear polarization surface enhanced NMR (DNP-SENS), Mossbauer spectroscopy, and computational chemistry were combined to obtain structural information on the active-site speciation in Sn-beta zeolite. This approach unambiguously shows the presence of framework Sn-IV-active sites in an octahedral environment, which probably correspond to so-called open and closed sites, respectively (namely, tin bound to three or four siloxy groups of the zeolite framework).