The structural and vibrational properties of amorphous germanium oxide (a-GeO 2 ) are investigated using first-principles calculations based on density functional theory. We first generate an a-GeO 2 structure by first-principles molecular dynamics and analyze its structural properties. The vibrational spectra is then calculated within a density-functional approach. Both static and dynamic properties are in good agreement with experimental data. We next generate defects in our structure (oxygen vacancies with several density and charge states) and consider the most stable atomic configurations, focusing on the vibrational features of threefold coordinated O and divalent Ge centers.