The Principality of Transylvania (Hungarian: Erdélyi Fejedelemség; Latin: Principatus Transsilvaniae; German: Fürstentum Siebenbürgen; Romanian: Principatul Transilvaniei / Principatul Ardealului; Turkish: Erdel Voyvodalığı / Transilvanya Prensliği) was a semi-independent state ruled by Hungarian princes. It existed as an Ottoman vassal state for the majority of the 16th and 17th centuries, overseen by Ottoman Turkish sultans. At various points during this period, the Habsburgs also exerted a degree of suzerainty in the region. Its territory, in addition to the traditional Transylvanian lands, also included the other major component called Partium, which was in some periods comparable in size with Transylvania proper. The establishment of the principality was connected to the Treaty of Speyer. However, Stephen Báthory's status as king of Poland also helped to phase in the name Principality of Transylvania.
The principality continued to be a part of the Lands of the Hungarian Crown and was a symbol of the survival of Hungarian statehood. It represented Hungarian interests against Habsburg encroachments in the Habsburg-ruled Kingdom of Hungary. Traditional Hungarian law had to be followed scrupulously in the principality; furthermore, the state was predominantly Protestant. After the unsettled period of Rákóczi's War of Independence, it was subordinated to the Habsburg monarchy.