The bond distances and coordination numbers of the predominant Np(VII) complex in strongly alkaline solution have been determined using EXAFS transmission measurements. The stoichiometry and structure of NPO4(OH)(2)(3-) has been deduced by combining these data with different structure models, mostly determined by using DFT based methods, The experimental and theory based distance Np(VII)-O-oxo is 1.89(4) and 1.90 Angstrom, respectively, whereas the Np(VII)-OH- distance is 2.32(6) and 2.33 Angstrom, respectively. Theory based geometry and bond distances have been obtained also for other Np(VII) and Np(VI) complexes, NpO2(OH)(4)(-), NpO4-, NPO4(OH)(2)(4-), and NpO2(OH)(4)(2-), NPO42-. The "NPO6" - unit has a square bipyramidal geometry both in NpO4(OH)(2)(3-/4-) and in NpO2(OH)(4)(1-/2-), albeit with some difference in bond distances. The close similarity in structure indicates that no major rearrangements are necessary on electron transfer between Np(VI) and Np(VII), a possible explanation for the stable and reproducible Np(VII)/Np(VI) redox potential observed in alkaline solution. The structure data indicate that new Np(VII) species may be identified by oxidation of Np(VI) solutions at lower hydroxide concentrations.