Line S1 is a S-Bahn line on the Rhine-Ruhr network. It is operated by DB Regio. It runs from Dortmund via Bochum and Essen to Duisburg. From there it travels south to Düsseldorf and Hilden before continuing to Solingen. It is operated on weekdays at 15-minute intervals between Dortmund Hbf and Essen Hbf, at 20-minute intervals between Düsseldorf Hbf and Solingen and at 30-minute intervals between Düsseldorf and Essen, using coupled sets of class 422 four-car electrical multiple units.

The Rhine-Ruhr S-Bahn is a polycentric and electrically driven S-bahn network covering the Rhine-Ruhr Metropolitan Region in the German federated state of North Rhine-Westphalia. This includes most of the Ruhr, the Berg cities of Wuppertal and Solingen and parts of the Rhineland. The easternmost city within the S-Bahn Rhine-Ruhr network is Unna, the westernmost city served is Mönchengladbach.