Custodian of the Two Holy Mosques is a title given to the King of Saudi Arabia. It is a new term, and was not used in the past. Since the formation of Saudi Arabia occurred a few years after the abolition of the Islamic Caliphate, the title was created to give a sense of legitimacy to the King as a protector of the two holy cities of Mecca and Madinah, which had traditionally been the role of the Caliph.

Some have charged that this invention was carried out by the Saudi monarchy so that it could try to replace the Caliphate. The reason why the Saudi monarch didn't declare himself the Caliph was due to the fact the Saudi tendency to follow the Wahhabi vision of Islam, and such a move would thus be rejected by most Muslims. This is the view at least, of opponents of the Saudi regime and Wahhabism.