X-ray spectroscopic techniques have been used in the studies of electronic and structural properties of nonstoichiometric TiO_2−x thin films obtained by reactive sputtering from Ti target. Films characterisation has been completed by means of X-ray diffraction in grazing incidence, GID, UV Raman and impedance spectroscopy, optical spectrophotometry, 1s3p Resonant X-ray Emission Spectroscopy, RXES, and X-ray Photoelectron Spectroscopy, XPS. Stoichiometric thin films of TiO₂ are composed of a well-crystallised anatase–rutile mixture with the predominance of anatase while the films with higher oxygen deficit are amorphous to larger extent. Oxidation state changes from Ti⁴⁺ in stoichiometric films towards Ti³⁺ upon increasing departure from stoichiometric composition. This change is accompanied by the significant decrease in the electrical resistivity. The comparison of band gap energies, determined independently from optical and valence band X-ray absorption/emission spectra is good assuming direct allowed transitions.