The Ruhr, also referred to as the Ruhr area, sometimes Ruhr district, Ruhr region, or Ruhr valley, is a polycentric urban area in North Rhine-Westphalia, Germany. With a population density of 2,800/km2 and a population of over 5 million (2017), it is the largest urban area in Germany. It consists of several large cities bordered by the rivers Ruhr to the south, Rhine to the west, and Lippe to the north. In the southwest it borders the Bergisches Land. It is considered part of the larger Rhine-Ruhr metropolitan region of more than 10 million people, which is the third largest in Western Europe, behind only London and Paris.

North Rhine-Westphalia or North-Rhine/Westphalia, commonly shortened to NRW, is a state (Land) in Western Germany. With more than 18 million inhabitants, it is the most populous state in Germany. Apart from the city-states, it is also the most densely populated state in Germany. Covering an area of 34,084 square kilometres (13,160 sq mi), it is the fourth-largest German state by size.