The Principality of Brunswick-Wolfenbüttel (German: Fürstentum Braunschweig-Wolfenbüttel) was a subdivision of the Duchy of Brunswick-Lüneburg, whose history was characterised by numerous divisions and reunifications. Various dynastic lines of the House of Welf ruled Brunswick-Wolfenbüttel until the dissolution of the Holy Roman Empire in 1806. As a result of the Congress of Vienna, its successor state, the Duchy of Brunswick, was created in 1815.
After Otto the Child, grandchild of Henry the Lion, had been given the former allodial seat of his family (located in the area of present-day eastern Lower Saxony and northern Saxony-Anhalt) by Emperor Frederick II on 21 August 1235 as an imperial enfeoffment under the name of the Duchy of Brunswick-Lüneburg, the duchy was divided in 1267/1269 by his sons.
Albert I (also called Albert the Tall) (1236-1279) was given the regions around Brunswick-Wolfenbüttel, Einbeck-Grubenhagen and Göttingen-Oberwald. He thus founded the Old House of Brunswick and laid the basis for what became, later, the Principality of Brunswick-Wolfenbüttel. His brother John (1242-1277) inherited the land around Lüneburg and founded the Old House of Lüneburg. The town of Brunswick remained under joint rule.
The area of Brunswick(-Wolfenbüttel) was further subdivided in the succeeding decades. For example, the lines of Grubenhagen and Göttingen were split for a while. In a similar way, in 1432 the estates between the Deister hills and the Leine river, that had been gained in the meantime from the Middle House of Brunswick, split away to form the Principality of Calenberg. There were further reunifications and divisions. Following the twelfth division of the duchy in 1495, whereby the Principality of Brunswick-Calenberg-Göttingen was re-divided into its component territories, Duke Henry the Elder was given the land of Brunswick, to which the name of the new Residenz at Wolfenbüttel was added. From then on the name of the principality became "Brunswick-Wolfenbüttel".
As a result of the German Mediatisation of 25 February 1803 the principality was given the territories of the secularised imperial abbeys of Gandersheim and Helmstedt. In 1806 Duke Charles William Ferdinand was mortally wounded as a Prussian general in the Battle of Auerstedt. After a short interregnum Brunswick was occupied from 1807 to 1813 by the French and became part of the Kingdom of Westphalia.
After the end of Napoleonic rule the state was re-established under the name of the Duchy of Brunswick.