Montségur (French pronunciation: [mɔ̃seɡyʁ]; Languedocien: Montsegur) is a commune in the Ariège department in southwestern France.

It is famous for its fortification, the Château de Montségur, that was built on the "pog" (mountain) on the ruins of one of the last strongholds of the Cathars.

The earliest signs of settlement in the area date back to the time of the Neanderthals, tens of thousands of years ago.

The name "Montségur" comes from Latin mons securus ("secure mountain") which evolved into mont ségur in Occitan.

In March 1244, the Cathars finally surrendered and approximately 244 were burned en masse in a bonfire at the foot of the pog when they refused to renounce their faith.