The　structural　stability　of　hexagonal　tungsten　mononitride　(WN)　has　been　studied　combining　scanning　transmission　electron　microscopy　and　first-principles　calculations.　The　results　show　that　the　WC-type　WN　with　vacancies　of　6　similar　to　8　at%　is　more　stable　than　the　previously　proposed　MnP-type　and　NiAs-type　structures.　Due　to　the　larger　vibrational　entropy　of　the　WC-type　WN,　the　vacancy　concentration　required　to　stabilize　the　WC-type　structure　is　lower　at　high　temperatures.　The　results　demonstrate　the　importance　of　vacancies　and　configurational　and　vibrational　entropies　in　the　structural　stability　of　compounds　synthesized　at　high　temperatures.