The Ottoman Caliphate (Ottoman Turkish: خلافت مقامى, romanized: hilâfet makamı, lit. 'office of the caliphate') was the claim of the heads of the Turkish Ottoman dynasty, rulers of the Ottoman Empire, to be the caliphs of Islam during the late medieval and early modern era.

Ottoman rulers first assumed the style of caliph in the 14th century, though did at that point not claim religious authority beyond their own borders. After the conquest of Mamluk Egypt by Sultan Selim I in 1517 and the abolition of the Mamluk-controlled Abbasid Caliphate, Selim and his successors ruled one of the strongest states in the world and gained control of Mecca, Medina and Jerusalem, the religious and cultural centers of Islam. The claim to be caliphs transitioned into a claim to universal caliphal authority, similar to that held by the Abbasid Caliphate prior to the sack of Baghdad in 1258. Further Ottoman victories, the dynasty's geopolitical dominance in the 16th–17th centuries, and the lack of rival claimants strengthened the Ottoman claim to be the leaders of the Muslim world.

Following territorial losses in the 18th and 19th centuries, the use of caliphal authority by the Ottomans reached its height under Abdul Hamid II (r. 1876–1909), who attempted to cultivate support for the Ottoman Empire through a Pan-Islamist foreign policy. Abdul-Hamid's absolutist rule came to an end through the Young Turk Revolution of 1908. The caliphal office was weakened in domestic politics, though was retained due to its usefulness in international diplomacy. At the beginning of World War I, Sultan Mehmed V proclaimed a jihad against the Entente, though this was largely ineffectual. The legitimacy and authority of the Ottoman Caliphate was damaged by the Great Arab Revolt (1916–1918) and the end of the war, which saw the empire lose all of its Arab territories.

The Ottoman Empire came to an end following the partition of the Ottoman Empire and the Turkish War of Independence (1919–1922), which established the modern Republic of Turkey. The last Ottoman caliph, Abdülmecid II, retained his position under the republic until the abolition of the caliphate on 3 March 1924, as part of Mustafa Kemal Atatürk's secular reforms. The imperial Osmanoğlu family was also exiled from Turkey.

With the establishments of Sufi orders like the Bayramiyya and Mawlawiyya under the Ottoman Caliphate, the mystical side of Islam, Sufism, flourished.

Several early Ottoman sultans claimed the style of caliph. Murad I (r. 1362–1389) was notably often referred to by this title from his conquest of Adrianople in the 1360s onwards. Murad achieved some international recognition of this title, for instance from the Karamanids in correspondence. The title was used consistently by sultans from at least the time of Murad II (r. 1421–1444; 1446–1451) onwards. Mehmed II (r. 1444–1446; 1451–1481) was referred to as a caliph in contemporary sources and he used the typically caliphal title of amir al-Mu'minin. Prior to 1517, Selim I had ordered that the khutbah be recited in his name as Ottoman caliph several times, for instance at Tabriz in 1514 and at Aleppo in 1516.

Although some Sunni Muslims in Iran and Central Asia recognized the Ottomans as religious leaders of Islam in the 15th and 16th centuries, their use of the caliphal title did for the most part not carry real religious or political significance. The Ottomans were not the only Muslim rulers to use the title and in the eyes of most contemporary Muslim jurists, the caliphate had come to an end with the death of the Abbasid caliph al-Musta'sim during the Mongol sack of Baghdad in 1258. The Abbasid Caliphate was restored in Cairo under the Mamluk Sultanate in 1261, when Sultan Baybars named Al-Mustansir II, who claimed Abbasid descent, as caliph. This second line of Abbasid caliphs however had no significant authority in Egypt or elsewhere. The use of the title of caliph by other Muslim rulers was a development that also began after 1258; in-line with the ideas of the theologian Jalal al-Din Davani, a solution to the end of the universal Abbasid Caliphate was that Muslim rulers take power as imams (religious leaders) within their own domains. Such "caliphs" were thus only caliphs in their own territories, not claiming universal religious authority.

In 1517, Selim I defeated the Mamluk Sultanate in the Ottoman–Mamluk War. The Sharif of Mecca submitted himself to Selim and sent the keys of the Kaaba to the sultan. Selim thus assumed the title of Custodian of the Two Holy Mosques. The conquest of Egypt made the Ottoman Empire one of the largest states in the world, and it had also gained control of Mecca and Medina, the religious and cultural centers of Islam.