Transylvania (Romanian: Transilvania or Ardeal; Hungarian: Erdély; German: Siebenbürgen or Transsilvanien) is a historical and cultural region in Central-Eastern Europe, encompassing central Romania. To the east and south its natural border is the Carpathian Mountains and to the west the Apuseni Mountains. Broader definitions of Transylvania also include the western and northwestern Romanian regions of Crișana and Maramureș, and occasionally Banat. Historical Transylvania also includes small parts of neighbouring Western Moldavia and even a small part of south-western neighbouring Bukovina to its north east (represented by Suceava County).

Transylvania is known for the scenery of its Carpathian landscape and its rich history, coupled with its multi-cultural character. It also contains Romania's second-largest city, Cluj-Napoca, and other very well preserved medieval iconic cities and towns such as Brașov, Sibiu, Târgu Mureș, Alba Iulia, Mediaș, and Sighișoara. It is also the home of some of Romania's UNESCO World Heritage Sites such as the Villages with fortified churches, the Historic Centre of Sighișoara, the Dacian Fortresses of the Orăștie Mountains and the Roșia Montană Mining Cultural Landscape.

It was under the rule of the Agathyrsi, part of the Dacian Kingdom (168 BC–106 AD), Roman Dacia (106–271), the Goths, the Hunnic Empire (4th–5th centuries), the Kingdom of the Gepids (5th–6th centuries), the Avar Khaganate (6th–9th centuries), the Slavs, and the 9th century First Bulgarian Empire. During the late 9th century, Transylvania was reached and conquered by the Hungarian tribes, and Gyula's family from seven chieftains of the Hungarians ruled it in the 10th century. King Stephen I of Hungary asserted his claim to rule all lands dominated by Hungarian lords. He personally led his army against his maternal uncle Gyula III and Transylvania became part of the Kingdom of Hungary in 1002.

After the Battle of Mohács in 1526 it belonged to the Eastern Hungarian Kingdom, from which the Principality of Transylvania emerged in 1570 by the Treaty of Speyer. During most of the 16th and 17th centuries, the principality was a vassal state of the Ottoman Empire; however, the principality had dual suzerainty (Ottoman and Habsburg).

In 1690, the Habsburg monarchy gained possession of Transylvania through the Hungarian crown. After the failure of Rákóczi's War of Independence in 1711, Habsburg control of Transylvania was consolidated, and Hungarian Transylvanian princes were replaced with Habsburg imperial governors. During the Hungarian Revolution of 1848, the Hungarian government proclaimed union with Transylvania in the April Laws of 1848. After the failure of the revolution, the March Constitution of Austria decreed that the Principality of Transylvania be a separate crown land entirely independent of Hungary. The separate status of Transylvania ended with the Austro-Hungarian Compromise of 1867, and it was reincorporated into the Kingdom of Hungary (Transleithania) as part of the Austro-Hungarian Empire. After World War I, the National Assembly of Romanians from Transylvania proclaimed the Union of Transylvania with Romania on 1 December 1918, and Transylvania became part of the Kingdom of Romania by the Treaty of Trianon in 1920. In 1940, Northern Transylvania reverted to Hungary as a result of the Second Vienna Award, but it was returned to Romania after the end of World War II.

In popular culture, Transylvania is commonly associated with vampires, due to the influence of Bram Stoker's 1897 novel Dracula and the many subsequent books and films that the story has inspired.