The Principality of Transylvania (German: Fürstentum Siebenbürgen; Hungarian: Erdélyi Fejedelemség; Latin: Principatus Transsilvaniae; Romanian: Principatul Transilvaniei or Principatul Ardealului) was a semi-independent state, ruled primarily by Hungarian princes. Its territory, in addition to the traditional Transylvanian lands, also included eastern regions of Hungary, called Partium. The establishment of the principality was connected with Treaty of Speyer. However Stephen Báthory's status as king of Poland also helped to phase in the name Principality of Transylvania. It was usually under the suzerainty of the Ottoman Empire; however, the principality often had dual vassalage (Ottoman Turkish sultans and the Habsburg Hungarian kings) in the 16th and 17th centuries.
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 the Hungarian interests against Habsburg encroachments in Habsburg ruled Kingdom of Hungary. All traditional Hungarian law remained to be followed scrupulously in the principality; furthermore, the state was imbued with a preponderantly Protestant feature. After the unsettled period of Rákóczi's War of Independence, it was turned to the Habsburg Monarchy.