It is located in Central and Eastern Europe. The Danube was once a long-standing frontier of the Roman Empire, and today flows through 10 countries, more than any other river in the world.

The Danube River holds the world record for flowing through or along the borders of the most countries. Starting in the Black Forest of Germany, this historic waterway traverses a total of ten nations: Germany, Austria, Slovakia, Hungary, Croatia, Serbia, Romania, Bulgaria, Moldova, and Ukraine. It serves as a vital artery for European trade, culture, and tourism, connecting major capital cities like Vienna, Bratislava, Budapest, and Belgrade. The river eventually empties into the Black Sea via the Danube Delta, a UNESCO World Heritage site. Because it acts as a natural border for so much of its length, the Danube is often referred to as the "International River." In 2026, it remains the most popular destination for European river cruising, allowing travelers to experience a vast array of diverse languages, cuisines, and histories in a single journey. Its unique status as a shared resource requires extensive international cooperation for environmental protection and navigation management across all ten sovereign territories.