The Breg is a river, 46 kilometres long, in Baden-Württemberg, Germany, and the primary headstream of the Danube.

Baden-Württemberg, commonly shortened to BW or BaWü, is a German state in Southwest Germany, east of the Rhine, which forms the southern part of Germany's western border with France. With more than 11.07 million inhabitants as of 2019 across a total area of nearly 35,752 km2 (13,804 sq mi), it is the third-largest German state by both area and population. As a federated state, Baden-Württemberg is a partly-sovereign parliamentary republic. The largest city in Baden-Württemberg is the state capital of Stuttgart, followed by Mannheim and Karlsruhe. Other major cities are Freiburg im Breisgau, Heidelberg, Heilbronn, Pforzheim, Reutlingen, Tübingen, and Ulm.