This article reports on the structure and mechanical properties of CNx thin films deposited by unbalanced reactive magnetron sputtering of C in N-2 discharges. The films were grown on Si(001) substrates kept at temperatures (T-s) between 150 and 600 degrees C. Depending on T-s, the films contained between 15 and 26 at. % N. X-ray photoelectron spectroscopy of samples typically showed two peaks in the C 1s core level spectrum (centered at 284.5 and 286.2 eV) and two peaks in the N 1s core level spectrum (centered at 398.4 and 400.3 eV). This indicates that there are two types of C-N bonds where N is bonded to both sp(2)- and sp(3)-coordinated C atoms in the as-deposited films. Transmission electron microscopy showed that the films produced in the temperature range 200 less than or equal to T-s less than or equal to 600 degrees C had a highly textured, turbostraticlike structure with the c axis in the plane of the film. The basal planes in this structure were found to be buckled and bent due to incorporation of N in substitutional sites. By contrast, films produced at T-s = 150 degrees C were generally amorphous, but contained -3 nm diamond clusters. The mechanical properties were evaluated in nanoindentation experiments. Load versus deflection curves showed that the 0.3 mu m films grown at T-s greater than or equal to 200 degrees C had very high elastic recoveries with values up to 85% of the total indentation displacement. Analyses of the shapes of the load versus deflection curves, using a modeling approach that takes into account the elastic and plastic properties of both the film and the substrate, indicate that the contact deformation of the CN, films was predominantly elastic and the films’ hardness values were estimated to be in the range 40-60 GPa. The high hardness and elasticity are proposed to be due to the buckling of the graphitic basal planes, resulting in a structure where the sp(2)-bonded basal planes are terminated with N bonded to sp(3)-hybridized carbon atoms that result in a dense, three dimensional, covalently bonded network.