The structure and dynamics of the limiting hydrated form of disodium hydrogen 12-tungstophosphoric acid (HNaPW) were investigated as a function of temperature using solid-state H-1, Na-23, and 11P nuclear magnetic resonance spectroscopy, infrared spectroscopy, and X-ray analysis. The H-1 nonspinning (NS) and magic-angle spinning (MAS) NMR results indicate that the limiting hydrated form of HNaPW has two types of protons. One type of proton corresponds to lone protons isolated from all other protons in the material. The second type of proton corresponds to an isolated proton pair of a water molecule. 1H NS NMR spectra recorded from 168 to 393 K, in combination with theoretical simulations, show that the proton dynamics of the water molecule can be characterized by four temperature ranges above 168 K, the temperature corresponding to a rigid lattice. From 168 to 203 K, proton motion is minimal; from 203 to 293 K, the proton motion is dominated by rotational diffusion; from 293 to 383 K, both translational and rotational diffusion characterize the motion; above 383 K, the water molecule protons undergo chemical exchange with the lone protons of the material. The 23Na NS and MAS NMR results, along with simulations of the spectra based on the second-order quadrupolar frequency shift, indicate that two six-coordinate sodium sites are present in this material. The six nearest neighbors of each sodium cation are oxygen atoms. Na-23{H-1} spin-echo double-resonance (SEDOR) NMR and theoretical calculations show that sodium and proton sites are separated by at least 686 pm. The two sodium sites persist to temperatures near 383 K but the quadrupole coupling constant of each site decreases with temperature suggesting that the two sodium sites have increased mobility at higher temperature, possibly a result of lattice expansion. Results from P-31 NS and MAS NMR experiments show that there are three different four-coordinate phosphorus sites. The nearest neighbors of each phosphor-us site are oxygen atoms and each phosphorus site has local tetrahedral symmetry. A P-31{H-1} SEDOR experiment shows that all phosphor-us sites are coupled to 1H nuclei. Room-temperature H-1{P-31} rotational echo double-resonance (REDOR) NMR experiments show that the lone proton and water molecule protons are both coupled to two phosphorus sites. Both of these types of protons are part of the secondary structure of the Keggin anion and are in relative motion to the two P-31 sites. Infrared results show that the lone proton asymmetrically bridges four terminal oxygen atoms of the Keggin anion and that the water molecule protons are hydrogen bonded to terminal oxygen atoms of the Keggin anion. X-ray analysis shows that the unit cell has cubic symmetry with a cell parameter a = 1197 pm. Elemental analysis along with the results of NMR experiments show that the formula of the limiting hydrated form of this commercially available salt should be written as H(0.5)Na(2.5)PW(12)O(40)4H(2)O.