Tin phosphate glasses, of general formula xSnO·(1 - x)P2O5(0.3 < x < 0.8), have been prepared by conventional melt-quench techniques and their structures studied using 31P and 119Sn nuclear magnetic resonance. The distribution of [PO4] Qn species changes with composition in accordance with the simple binary model, and the changes in chemical shift can be explained by the redistribution of electron charge from the P=O double bond. Sn(II) is found to occupy a highly asymmetric site, typical of a sterically active lone pair of electrons. The 119Sn parameters of the chemical shift tensor change systematically with x, reflecting the change in local environment from one where the next nearest neighbours are predominantly Q2 phosphorus to one where they are predominantly Q0 phosphorus.