It went operational shortly before Expo 2000 and is focused on the Hanover region, and also connects with adjacent districts (Celle, Hameln-Pyrmont, Hildesheim, Nienburg and Schaumburg), and into the state of North Rhine-Westphalia (Minden, Paderborn).

This led at first only to the establishment between 1965 and 1970 of regional commuter services on the east–west axis between Nienburg / Minden, Wunstorf, Hannover Hauptbahnhof (central station), Lehrte and Celle and on the Deister Railway.

In 1984, in preparation for the upgrading of the line between Wunstorf and Hannover, Seelze station was relocated and rebuilt with overtaking tracks.

After Hanover won the right to build Expo 2000 in 1990, it was decided to bring forward the planned introduction of an S-Bahn network that was originally intended to be opened at a later date.

On 12 November 1990 a development agreement was signed between the state of Lower Saxony, the Municipal Association of Greater Hannover and Deutsche Bundesbahn.

In a relatively short time lines which for decades had remained virtually unchanged were upgraded considerably in and around Hanover.

In Leinhausen an extensive flying junction was built; this separates regional and long distance traffic running to and from the north and west.

On the Deister Railway a 10 km (6.2 mi) long section of double track was built between Lemmie and Egestorf to the west of the Weetzen level crossing in order to avoid delays due to conflicting train movements.

[1] The Hannover S-Bahn serves 12 stations within Hanover and connects the state capital with suburbs and other towns in the area.

These differ from the vehicles of class 423, as they have a lower floor height of 80 cm, fewer doors and include toilets.

Although delivery began as early as 1998, the class 424 trains were not yet ready for the opening of the S-Bahn network at the start the Expo 2000 due to technical problems.