The Duchy of Brunswick-Lüneburg, or more properly the Duchy of Brunswick and Lüneburg, was a historical duchy that existed from the late Middle Ages to the Late Modern era within the Holy Roman Empire, until the year of its dissolution. The duchy was located in what is now northwestern Germany. Its name came from the two largest cities in the territory: Brunswick and Lüneburg.

Braunschweig or Brunswick is a city in Lower Saxony, Germany, north of the Harz Mountains at the farthest navigable point of the river Oker, which connects it to the North Sea via the rivers Aller and Weser. In 2016, it had a population of 250,704.