Joseph Freiherr von Hammer-Purgstall (June 9, 1774 – November 23, 1856) was an Austrian orientalist.

Born Joseph Hammer in Graz, Styria, he received his early education mainly in Vienna. Entering the diplomatic service in 1796, he was appointed in 1799 to a position in the Austrian embassy in Constantinople, and in this capacity he took part in the expedition under Admiral Sir William Sidney Smith and General Sir John Hely-Hutchinson against the French. In 1807 he returned home from the East, after which he was made a privy councillor, and, on inheriting, in 1835, the estates of the Countess Purgstall in Styria, was given the title of Freiherr.

For fifty years Hammer-Purgstall wrote incessantly on the most diverse subjects and published numerous texts and translations of Arabic, Persian and Turkish authors. It was natural that a scholar who traversed so large a field should lay himself open to the criticism of specialists, and he was severely handled by Friedrich Christian Diez (1794-1876), who, in his Unfug und Betrug (1815), devoted to him nearly 600 pages of abuse.

Hammer-Purgstall did for Germany the same work that Sir William Jones did for England and Silvestre de Sacy for France. He was, like his younger but greater English contemporary, Edward William Lane, with whom he came into friendly conflict on the subject of the origin of The Thousand and One Nights, an assiduous worker, and in spite of many faults did more for oriental studies than most of his critics put together.

Hammer-Purgstall's principal work is his Geschichte des osmanischen Reiches (10 vols., 1827-1835). Among his other works are Constantinopolis und der Bosporos (1822); Sur les origines russes (St Petersburg, 1825);
The longest single English translation of Evliya Celebi's travelogue Seyahatname was published in 1834. Von Hammer's work covers the first two volumes: Istanbul and Anatolia. The translation is somewhat inaccurate and uses a bizarre transliteration system. It is out of print but can be found in some university libraries under the author name, "Evliya Efendi."
He also published Geschichte der osmanischen Dichtkunst (1836); Geschichte der Goldenen Horde in Kiptschak (1840); Geschichte der Chane der Krim (1856); and an unfinished Litteraturgeschichte der Araber (1850-1856). He also wrote Khlesls, des Cardinals Leben. Mit der Sammlung von Khlesls Briefen und anderen Urkunden (4 vols., 1847-1851), a four volume biography of Melchior Cardinal Khlesl.

Hammer-Purgstall supported the foundation of the Österreichische Akademie der Wissenschaften (en: Austrian Academy of Sciences) in Vienna and became the Academy's first president (1847-1849). The Austrian Orient society, Österreichische Orient-Gesellschaft Hammer-Purgstall, is named after him. It was founded in 1959 to foster cultural relations with the Near East and to attend to the needs of university students from the Near East studying in Austria.

He died in Vienna.