The annealing behaviour of cathodic are deposited amorphous carbon nitride films has been investigated for temperatures up to 1000 degrees C. The annealing of the films was performed in situ within a transmission electron microscope, and the structure was probed using electron energy loss spectroscopy. The as-deposited carbon nitride was found to have a [N]/[C] atomic ratio of 0.45 with both the carbon and nitrogen atoms bonded mainly in sp(2) configurations. As the anneal temperature was increased to 200 degrees C, the [N]/[C] ratio decreased to 0.35 due to the removal of loosely bound nitrogen from the amorphous network. For anneal temperatures above 400 degrees C, the [N]/[C] ratio gradually decreases as the carbon nitride film graphitises, forcing nitrogen out of the structure. There was no evidence for the formation of nitrogen containing crystallites during the annealing process.