The Unification of Bulgaria (Bulgarian: , Saedinenie na Balgariya) was the act of unification of the Principality of Bulgaria and the province of Eastern Rumelia in the autumn of 1885. It was co-ordinated by the Bulgarian Secret Central Revolutionary Committee (BSCRC). Both had been parts of the Ottoman Empire, but the Principality had functioned de facto independently whilst the Rumelian province was autonomous and had an Ottoman presence. The Unification was accomplished after revolts in Eastern Rumelian towns, followed by a coup on 18 September [O.S. 6 September] 1885 supported by the Bulgarian Knyaz Alexander I. The BSCRC, formed by Zahari Stoyanov, began actively popularizing the idea of unification by means of the press and public demonstrations in the spring of 1885.

Eastern Rumelia (Bulgarian: Източна Румелия, Iztochna Rumeliya; Ottoman Turkish: روم الى شرقى‎, Rumeli-i Şarkî; Greek: Ανατολική Ρωμυλία, Anatoliki Romylia) was an autonomous province (oblast in Bulgarian, vilayet in Turkish) in the Ottoman Empire, created in 1878 by the Treaty of Berlin and de facto ended in 1885, when it was united with the Principality of Bulgaria, also under Ottoman suzerainty. It continued to be an Ottoman province de jure until 1908, when Bulgaria declared independence. Ethnic Bulgarians formed a majority of the population in Eastern Rumelia, but there were significant Turkish and Greek minorities. Its capital was Plovdiv (Ottoman Filibe, Greek Philippoupoli). The official languages of Eastern Rumelia were: Bulgarian, Greek and Ottoman Turkish.