The atomic scale structure of network glass forming systems with the AX₂ stoichiometry is considered and particular attention is paid to the systems GeSe₂, ZnCl₂ and GeO₂ for which the partial-pair correlation functions have been measured by using the method of isotopic substitution in neutron diffraction. The basic structural motif in all of these systems is the A(X_1/2)₄ tetrahedron, although homopolar bonds are also a significant feature in the case of liquid and glassy GeSe₂. The structural motifs link to form a network in which ordering occurs on two different length scales at distances greater than the nearest-neighbour. One of these length scales is associated with an intermediate range and manifests itself by the appearance of a so-called first sharp diffraction peak in the measured diffraction patterns at a scattering vector k_FSDP where and r_AX is the nearest-neighbour distance for unlike chemical species. The other is associated with an extended range, which has a periodicity given by , where k_PP denotes the scattering vector of the principal peak and . The nature and interplay between the ordering on the intermediate and extended length scales is characterized and discussed.