Ammonium tungsten bronze, (NH 4) x WO 3, has been prepared and studied by X ray, and steady-state and pulsed nuclear magnetic resonance techniques. It has the hexagonal bronze structure. Motional narrowing of the steady-state proton resonance line, corresponding to ionic diffusion, occurs near 200°K. Linewidth vs temperature data yields an Arrhenius activation energy for diffusion of 0.081 eV/ion. A two-pulse technique was used to measure the proton T 1 vs temperature over the range 87–323°K. Evidence for at least two T 1 minima was obtained, one below 85°K due to relaxation presumably caused by ammonium ion rotation with an associated energy barrier of 0.023 eV/ion. Another occurs near 215°K and is due to relaxation related to ionic translation. The motional narrowing experiment infers the presence of another diffusion mechanism, and a related T 1 minimum at temperatures greater than 215°K. Using an adiabatic demagnetization method, the temperature dependence of the correlation time for ionic jumps was also measured. The activation energy for ionic motion obtained from the T 1 data was about 0.075 eV/ion, and from the adiabatic demagnetization experiment was 0.065 eV/ion. With the information at hand it is not possible to identify which of the translational relaxation mechanisms is reflected in the adiabatic demagnetization data. The several possible mechanisms for ionic motion in this crystal structure are discussed, including the feasibility of dissociative equilibrium.