Ion dynamics in the highly conductive glassy fast ionic conductor, 0.7Li 2S + 0.3B 2S 3, were studied with NMR line width and nuclear spin-lattice relaxation, R 1( ω, T), of both mobile 7Li and immobile 11B nuclei, NMR pulsed field gradient diffusivity, and electrical (ionic) conductivity, σ( ω, T) over wide ranges of temperature and frequency. Some measurements were also done in 0.65Li 2S + 0.35B 2S 3. The quadrupolar split NMR spectrum of the 11B indicated that about 80% of the boron were in BS 3 groups and 20% were in BS 4 groups, and their relaxations could be resolved. We fitted R 1Li with a double-peaked distribution, Z Li, of activation energies, E a for the hops, where the peaks are due to the differing environments near BS 3 and BS 4. The conductivity, σ( ω, T), was calculated quantitatively from Z Li( E a) in our model with random walk and percolation over the lowest barriers. The apparent correlation time τ B (3) derived from spin-lattice relaxation of 11B in trigonal BS 3 groups, R 1B(BS 3) , were much shorter than τ B (4) from R 1B(BS 4) , which again were shorter than τ Li from R 1Li, although all relaxations are due to fluctuating electric field gradients from the hopping Li + ions. The times, τ Li, are those of single ion hopping, while times τ B are due to the fluctuations of the electric field gradient at the BS x groups which was due to the combined effect of several Li + ions hopping and to the interaction of the Li + ion with the BS x groups where x = 3 or 4. The 7Li NMR line narrowing and diffusivity yielded additional information on the correlation time for Li + hopping motion which are consistent, within our model, with the σ( ω, T) and R 1( ω, T) data.