Alkali aluminophosphate glasses, including those in the system xAl2O3·(1-x)CsPO3 (0 ≤ x ≤ 0.25), were examined by high-performance liquid chromatography (HPLC), infrared (IR), and 27Al magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopies. Phosphate anions become progressively shorter with the addition of alumina to a metaphosphate glass. Al3+ ions are initially incorporated into the structure in octahedral sites, but the average Al coordination number (CN) decreases with increasing alumina content and tetrahedral species are the preferred moiety when [O]/[P] > 3.5. Al[4] sites appear to be associated with monophosphate (Q0) anions. The role of modifier size on aluminophosphate structure is investigated. At low alumina content (< 15 mol%), the disproportionation of pyrophosphate anions into triphosphate and orthophosphate anions is responsible for the lower average Al CN of cesium aluminophosphate glasses compared with sodium aluminophosphate glasses.