Blaj (Romanian pronunciation: [blaʒ]; archaically spelled as Blaș; Hungarian: Balázsfalva; German: Blasendorf; Transylvanian Saxon: Blußendref) is a city in Alba County, Transylvania, Romania. It has a population of 17,816 inhabitants as of 2021.

The city administers eight villages: Deleni-Obârșie (Obursatanya), Flitești, Izvoarele (until 1960 Ciufud; Csufud), Mănărade (Monora), Petrisat (Magyarpéterfalva), Spătac (Szászpatak), Tiur (Tűr), and Veza (Véza).

The city was the principal religious and cultural center of the Romanian Greek-Catholic Church in Transylvania.

Blaj is first mentioned in 1271 as Villa Herbordi, after the deed of a Count Herbod. In 1313, the domain passed to Herbod's son Blasius Cserei and the town was mentioned as Blasii. Starting as a hamlet for the twenty families of servants of the noble's court, it was awarded town status on May 19, 1737.

The first public school in Romanian was established in Blaj in 1754. Blaj was the first place to have Romanian written with Latin alphabet instead of Cyrillic in which it had traditionally been written. Blaj was also a center for the Romanian Age of Enlightenment, being the founding site of the Transylvanian School that promoted the Roman cultural heritage of the Romanians. Thus Blaj gained the nickname "The Little Rome", as Romania's national poet Mihai Eminescu called it.

In 1848, Câmpia Libertății in Blaj was where over 40,000 Romanians met to protest Transylvania becoming a part of Hungary, holding that the lands would be stolen from them.

Blaj lies at the confluence of the Târnava Mare and Târnava Mică rivers, where they form the Târnava River. It is located 39 km (24 mi) northeast of the county seat, Alba Iulia, in a renowned wine-growing region.

Mănărade village (German: Donnersmarkt; Hungarian: Monor, during the Middle Ages, belonged to the Cistercian Igriș Abbey, a status attested from 1315-1320.