Exterminatus is an order to Destroy a planet in the Warhammer 40,000 universe. Typically used only as a last resort, when the price of holding or retaking the world is deemed to be too high, or the threat of mutation or heresy too great to contain by conventional means. Typically, the order may only be given by a high-ranking Imperial Warmaster, or a member of the Inquisition.

The Imperium has developed many ways of destroying a planet, from conventional firepower to specially-made weapons designed to annihilate a planet's surface or Ecosystem.