The line passes through Taunusstein, Bad Schwalbach (called Langenschwalbach until 1927), Aarbergen and Hahnstätten, which all lie in the Aar valley in the Western Hintertaunus (the lower north-western ridges of the Taunus).

The southern part of the Aar Valley Railway runs through Hesse and the section between Diez and Zollhaus lies in Rhineland-Palatinate.

Until 1951, passengers could change in Zollhaus to the narrow-gauge Nassau Light Railway (Nassauische Kleinbahn, NKB), connecting to Sankt Goarshausen and Braubach on the Rhine.

After the annexation of the Duchy of Nassau by the Kingdom of Prussia in 1866, the Prussian state railways considered build a rail link between Wiesbaden and the Limburg area.

Moritz Hilf, who had been technical director of the Nassau State Railway since 1862, was put in charge of building the line across the Taunus ridge and through the Aar valley.

This section was mainly used for the transport of minerals, which were obtained in the Zollhaus area (iron ore, limestone, marble and porphyry).

The line, which today is largely in the area of the municipalities of Hahnstätten and Diez, follows the relatively wide and flat Aar valley.

The line had to be realigned to connect to the new Central Station (Hauptbahnhof), opened in 1906, and Wiesbaden West freight yard.

A year later, the buildings and technical facilities of the line and stations were classified as a historical monument in anticipation of its closure.

The steep and winding line through the Eiserne Hand gap required the development of a short carriages with bogies, which was known as a Langenschwalbacher.

After the Second World War, the line was cut between Zollhaus and Kettenbach by the border between the American and French occupation zone.

[10] A proposed extension of the reactivated section of line to Michelbach was ruled out for cost reasons, since it would require a second vehicle.

[8] There have been plans since 1998 to restore and electrify the section of the Aar Valley Railway between Bad Schwalbach and Wiesbaden-Dotzheim as part of a proposed Wiesbaden Stadtbahn and building a new line from Dotzheim through the central city to Wiesbaden Central Station (Hauptbahnhof), including the option of an extension to Mainz.

However, another election in 2011 has changed the balance in the council and plans for a Stadtbahn have been revived, although the proposed initial stage would not connect to the Aar Valley Railway.