This file extension is used by the Warcraft 3: Frozen Throne, expansion to the Warcraft 3 strategy game. The file typically contains all the data needed for an entire campaign and will typically consist of a series of missions.

Although the campaigns that come with the Frozen Throne expansion package will use the W3N file type, the file type is also used for custom campaigns as well, which are created using the Warcraft 3 World Editor that comes with the Frozen Throne expansion.