The object of this experiment is to search for the structural origin of the intermediate phase by making careful measurements of the structure of glassy Ge-Se which is a prototypical covalently bonded network forming system for which the intermediate phase spans a wide composition window. Glasses associated with the intermediate phase are rigid but stress free and are optimally constrained i.e. the mean number of Lagrangian bonding constraints per atom is equal to the number of degrees of freedom. The results will be used to test first principles molecular dynamics models of the Ge-Se system which predict a plateau in a plot of the mean coordination number versus composition for glasses associated with the intermediate phase. The results will also be used to characterise both the intermediate and extended range atomic ordering.