The Grand Mosque seizure occurred during November and December 1979 when extremist insurgents calling for the overthrow of the House of Saud took over Masjid al-Haram, the holiest mosque in Islam, in Mecca, Saudi Arabia. The insurgents declared that the Mahdi (the "redeemer of Islam") had arrived in the form of one of their leaders – Mohammed Abdullah al-Qahtani – and called on Muslims to obey him. The Saudi army, advised by French commandos, fought for almost two weeks to reclaim the Grand Mosque.

The seizure of Islam's holiest site, the taking of hostages from among the worshippers and the deaths of hundreds of militants, security forces and hostages caught in the crossfire in the ensuing battles for control of the site, shocked the Islamic world. The siege ended two weeks after the takeover began and the mosque was cleared. Al-Qahtani was killed in the recapture of the mosque but leader Juhayman al-Otaybi and 67 of his fellow rebels who survived the assault were captured and later beheaded.Following the attack, the Saudi King Khaled implemented a stricter enforcement of Shariah (Islamic law) and he gave the ulama and religious conservatives more power over the next decade, and religious police became more assertive.