The NASA ATM (Air Traffic Management) Ontology describes classes, properties, and relationships relevant to the domain of air traffic management, and represents information pertinent to a broad and diverse set of interacting components in the US and the global airspace, including flights, aircraft, manufacturers, airports, airlines, air routes, facilities, air traffic advisories, weather phenomena, and many others. Three different variants of the ATM Ontology are provided: atmontoCore, atmonto, and atmontoPlus. The atmonto variant extends the core ontology by adding instances corresponding to key infrastructure components of the US National Airspace System (NAS).