The Rhein-Erft-Express is a Regional-Express service in the German states of North Rhine-Westphalia and Rhineland-Palatinate. It is numbered as line RE 8 and connects the cities of Mönchengladbach, Cologne, Bonn and Koblenz with each other and their surroundings, running hourly. It is complemented by a Regionalbahn stopping service, the Rhein-Erft-Bahn, running also between Mönchengladbach Hauptbahnhof and Koblenz Hauptbahnhof. On weekends it stops at some additional stations between Cologne Hbf and Koblenz Hbf. It is operated by DB Regio with Alstom Coradia Continental EMUs.

Köln Hauptbahnhof is the central railway station of Cologne, Germany. The station is an important local, national and international transport hub, with many ICE, Eurostar and Intercity trains calling there, as well as regional Regional-Express, RegionalBahn and local S-Bahn trains. EuroNight and Nightjet night services also call at the station. It has frequent connections to Frankfurt by way of the Cologne–Frankfurt high-speed rail line, which starts in southern Cologne. On an average day, about 280,000 travellers frequent the station, making it the fifth busiest station in Germany.