The Ruhr is an industrial area of Germany located in the state of North Rhine-Westphalia. It is one of the most densely populated and industrialized regions in Europe, and is home to many of Germany's largest cities, including Dortmund, Essen, Duisburg, Bochum, and Oberhausen. The Ruhr is known for its coal mining and steel production, and has been a major contributor to Germany's economic growth since the 19th century.