The Duchy of Brunswick-Wolfenbüttel was a historical state in northern Germany, established in the late Middle Ages. It was part of the larger Brunswick region and was ruled by the House of Welf. The duchy played a significant role in the political landscape of the Holy Roman Empire. The capital of the duchy was Wolfenbüttel, which became an important cultural and administrative center. The duchy was known for its contributions to education and the arts, particularly through the Wolfenbüttel Library, one of the oldest libraries in Germany. It existed until the early 19th century when it was absorbed into the Kingdom of Hanover.