S-Bahn

thumb|Diagram comparing typical rapid transit (U-Bahn, left) and S-Bahn (right) networks. The S-Bahn combines suburban branches into a high-frequency corridor across the city centre. Actual layouts vary by city. S-Bahn ( , ; ) is a type of hybrid commuter rail and rapid transit service, originating in German-speaking countries. In general, S-Bahn systems link suburbs with the city centre at moderate speeds, while continuing across the urban core over a central high-frequency corridor where multiple lines converge, where they provide a rapid means of travel across the city. The name S-Bahn derives from the German terms (), (), and (; not to be confused with the modern Stadtbahn).

The first such network, the Berlin S-Bahn, began operation in December 1930 and inspired similar systems across Europe. The term "S-Bahn" has since become a generic term for hybrid suburban–urban rail networks, with counterparts such as the Stog in Denmark, STrein/TrainS in Belgium, Esko/Slines in the Czech Republic, LineeS in Italy, and SKM in Poland. The S-Bahn is also recognized as a train category in several European countries. The concept also influenced systems outside the German-speaking world, including the Réseau Express Régional (RER) in Paris and its counterparts in other cities.