Solid state 11B, 27Al and 31P nuclear magnetic resonance spectroscopy has been used to study the microstructure of 16 Al2O3B2O3P2O5 glasses whose constituents may all act as glass formers. To obtain the fundamental parameters for the quadrupolar 27Al nuclei satellite transition spectroscopy has been applied. As a result, boron occurs always four-coordinated, while aluminium atoms are distinguished by three well defined environments assigned to four-, five- and six-coordination; the proportion of four-coordinated Al species decreases with increasing P2O5 content, that of five- and six-coordinated species increases. Phosphorus is tetrahedrally coordinated, its chemical shift varies systematically as a function of the bonding behavior in the second coordination sphere. The experimental findings can be described by a random network model for the whole glass-forming region, which includes a continuous transition from a silica-like structure of AlPO4 and BPO4 for [P2O5]/([B2O3] + [Al2O3(4)]) ratios of about 1, to a more loosened structure containing AlO4, AlO5 as well as Al(PO3)3 elements, if there is excess oxygen and this ratio becomes larger.