Alba Iulia (Romanian pronunciation: [ˌalba ˈjuli.a] ; German: Karlsburg or Carlsburg, formerly Weißenburg; Hungarian: Gyulafehérvár [ˈɟulɒfɛɦeːrvaːr]; Latin: Apulum) is a city that serves as the seat of Alba County in the west-central part of Romania. Located on the river Mureș in the historical region of Transylvania, it has a population of 64,227 (as of 2021).

During ancient times, the site was the location of the Roman camp Apulum. Since the High Middle Ages, the city has been the seat of Transylvania's Roman Catholic diocese. Between 1526 and 1570 it was the capital of the Eastern Hungarian Kingdom from which the Principality of Transylvania emerged by the Treaty of Speyer in 1570 and it was the capital of the Principality of Transylvania until 1711. At one point it also was a center of the Eastern Orthodox Metropolitan of Transylvania with suffragan to Vad diocese. On 1 December 1918, the Union of Transylvania with Romania was declared in Alba Iulia, and Romania's King Ferdinand I and, in 1922 Queen Marie were crowned in the Alba Iulia Orthodox Cathedral.

Alba Iulia is historically important for Romanians, Hungarians, and Transylvanian Saxons. In December 1918, Alba Iulia was officially declared Capital of the Great Union of Romania.

The city administers four villages: Bărăbanț (Borbánd), Micești (Ompolykisfalud), Oarda (Alsóváradja), and Pâclișa (Poklos).