We wish to better understand the interaction between the alkaline earth modifiers and the tellurite glass network. The aim is to relate structural changes in the glasses with the addition of modifier to the functional properties, such as Tg, density and optical properties. To achieve this we propose to study a series of alkaline-earth modified tellurite glasses, x MO.(1-x) TeO2, where M= Mg, Ca and Ba and x = 5-35 mol.%, using neutron diffraction. A combination of direct fitting, isostoichiometric differences and computational analysis will be used to determine the coordination numbers of tellurium, nTeO, and the alkaline earth modifiers, nmo.