We have used x-ray photoelectron spectroscopy to examine the structural environments of F and O in several series of SnF 2-SnO-P 2O 5 glasses. The F ls spectra indicate that F is incorporated primarily in F-P bonds in glasses containing 40 and 50 mol% P 2O 5, whereas F-Sn bonds coexist with F-P species in glasses with 30 mol% P 2O 5. The O ls spectra reveal that bridging oxygens (P-O-P) are consumed as SnF 2 replaces SnO. Using these results, along with reported Sn(II) crystal structures, we have developed a qualitative structural model that helps explain the composition/ property relationships of these interesting glasses. In particular, the lone electron pair typically associated with Sn(II) oxides and fluorides produces highly asymmetric Sn polyhedra which lead to high thermal expansions and low glass transition temperatures.