A systematic study of the chemical bonding in hydrogenated amorphous germanium-carbon (a-Ge1-xCx:H) alloys using X-ray photoelectron spectroscopy (XPS) is presented. The films, with carbon content ranging from 0 at. % to 100 at. %, were prepared by the rf co-sputtering technique. Raman spectroscopy was used to investigate the carbon hybridization. Rutherford backscattering spectroscopy (RBS) and XPS were used to determine the film stoichiometry. The Ge 3d and C 1s con levels were used for investigating the bonding properties of germanium and carbon atoms, respectively. The relative concentrations of C-Ge, C-C, and C-H bonds were calculated using the intensities of the chemically shifted C 1s components. It was observed that the carbon atoms enter the germanium network with different hybridization, which depends on the carbon concentration. For concentrations lower than 20 at. %, the carbon atoms are preferentially sp(3) hybridized, and approximately randomly distributed. As the carbon content increases the concentration of sp(2) sites also increases and the films are more graphitic-like.705581585