The glass forming region of the ZnO-Al2O3-P2O5 (ZAP) system was determined and the structures and properties of the glasses were characterized. For glasses with a constant O/P ratio, i.e., with similar average phosphate anion distributions, and with increasing alumina content, there is an increase in molar volume and glass transition temperature and a decrease in density and refractive index. The structures of the ZAP glasses were characterized by Raman spectroscopy, 31P and 27Al magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy, and high pressure liquid chromatography (HPLC). Systematically shorter phosphate anions constitute the structures of glasses with greater O/P ratios. The average aluminum coordination number (CNAl) changes systematically with composition, from ~ 4.0 to ~ 5.6, depending on the number of terminal oxygens available to coordinate each Al-cation. Glass properties are sensitive to both the types and concentrations of the P-anions as well as the CNAl. © 2013 Elsevier B.V.