The Cologne Bonn Region is a metropolitan area in North Rhine-Westphalia (NRW), Germany, covering the cities of Cologne, Bonn and Leverkusen, as well as the districts of Rheinisch-Bergischer Kreis, Oberbergischer Kreis, Rhein-Erft-Kreis and Rhein-Sieg-Kreis. The region covers an area of 3,839 km² with 3.13 million inhabitants. The city centres of Cologne and Bonn are 24 kilometres apart as the crow flies. At the outer city limits, there are only 8 kilometres between Cologne-Libur and Bonn-Geislar.

Cologne is the largest city of the German state of North Rhine-Westphalia and the fourth-most populous city of Germany with nearly 1.1 million inhabitants in the city proper and over 3.1 million people in the Cologne Bonn urban region. Cologne is also part of the Rhine-Ruhr metropolitan region, the second biggest metropolitan region by GDP in the European Union. Centered on the left (west) bank of the Rhine, Cologne is about 35 km (22 mi) southeast of the North Rhine-Westphalia state capital Düsseldorf and 25 km (16 mi) northwest of Bonn, the former capital of West Germany.