The Wupper-Express (RE 4) is a Regional-Express service in the German state of North Rhine-Westphalia (NRW) running between Aachen and Dortmund via Mönchengladbach, Düsseldorf, Wuppertal and Hagen.

It is the third most widely used Regional-Express line in the area administered by the Verkehrsverbund Rhein-Ruhr (VRR) with approximately 24,000 passengers a day.

Later, the end point was moved to Hamm and after the abolition of InterRegio services it was extended to Munster.

Under the second stage of North Rhine-Westphalia's integrated timetable (ITF 2), introduced in December 2002, it was replaced by the Maas-Wupper-Express (RE 13) and the Ems-Börde-Bahn (RB 89) services between Hagen and Munster and the Wupper-Express has since then run to Dortmund with a stop in Witten.

A reorganisation of services between Cologne and Dortmund is being undertaken in a program known as the Rhine-Ruhr Express (RRX).