Bulgaria (Bulgarian: България), officially the Republic of Bulgaria (Република България, Republika Bulgaria), a country in the Balkans in south-eastern Europe, borders five other countries: Romania to the north (mostly along the River Danube), Serbia and the Republic of Macedonia to the west, and Greece and Turkey to the south. The Black Sea defines the extent of the country to the east.

Bulgaria includes parts of the Roman provinces of Moesia, Thrace and Macedonia. Old European culture within the territory of present-day Bulgaria started to produce golden artifacts by the fifth millennium BC.

The emergence of a unified Bulgarian national identity and state date back to the early Middle Ages (7th century). All Bulgarian political entities that subsequently emerged preserved the traditions (in ethnic name, language and alphabet) of the First Bulgarian Empire (632/681 – 1018), which at times covered most of the Balkans and spread its alphabet, literature and culture among the Slavic and other peoples of Eastern Europe. Centuries later, with the decline of the Second Bulgarian Empire (1185 – 1396/1422), Bulgarian kingdoms came under Ottoman rule for nearly five centuries. The Russo-Turkish War of 1877-1878 led to the re-establishment of a Bulgarian state as a constitutional monarchy in 1878, with the Treaty of San Stefano marking the birth of the Third Bulgarian State. In 1908, with social strife brewing at the core of the Ottoman Empire, the Alexander Malinov government and Prince Ferdinand of Bulgaria formally proclaimed the full sovereignty of the Bulgarian state at the ancient capital of Veliko Turnovo. After World War II, in Bulgaria became a stalinist state and part of the Eastern Bloc. Todor Zhivkov dominated Bulgaria politically for 33 years (from to 1989). In 1990, after the Revolutions of 1989, the 'Communist Party' gave up its monopoly on power and Bulgaria transitioned to neo-liberalism and free-market capitalism.

As of Bulgaria functions as a parliamentary democracy within a unitary constitutional republic. A member of the European Union, NATO and the World Trade Organization, it has a high Human Development Index of 0.834, ranking 56th in the world in.