Vibrational spectroscopy and various physical property measurements (density, molar volume and glass transformation temperature) were used to investigate the structural changes that occurred with changes in composition for glasses prepared by standard melting and quenching techniques in the PbO-Bi2O3-GeO2 system. Regions of constant glass transformation temperature (Tg) were noted for these glasses at high GeO2 compositions, as determined from DSC measurements. These results clearly indicated the presence of amorphous phase separation. A model was proposed that could qualitatively interpret both the infrared and Raman spectra, and the molar volume data. At low lead oxide and bismuth oxide concentrations, lead acted primarily as a network modifier while bismuth acted as a mixed network former and modifier. At high concentrations, both lead and bismuth acted as network formers in linking discrete GeO4-units and possibly forming a lead oxide/bismuth oxide portion of the network. The observed results were also interpreted on the basis of Ge-O bonds involving bridged and non-bridged oxygen atoms, and on the basis of a possible change in coordination for germanium from four to six with metal oxide additions.