The S8 service of the S-Bahn Rhein-Main system bearing the KBS (German scheduled railway route) number 645.8.

In a short section between Mühlberg and Offenbach-Kaiserlei a line parallel with the South Main railway is used.

After the opening of the Frankfurt Citytunnel the service was renamed to S14 and extended to the new Hauptwache underground station.

Further extensions of the tunnel followed in 1983 (Konstablerwache) and 1990 (Ostendstraße and Lokalbahnhof) so that the Südbahnhof (South station) became the S14's eastern terminal.

In 1995 both services S14 and S15 were renamed to S8 and extended their operation to the east connecting the Central Station of Hanau.