The Mering–Weilheim railway (German: Ammerseebahn) is a 54 km long single-tracked main line in the provinces of Swabia and Upper Bavaria in southern Germany.

Until the early 1990s there were still long-distance trains (the FD-Züge) on the line that did not take the 'bypass' via Munich on their way from the north of Germany to Garmisch-Partenkirchen, but went directly from Augsburg along the Ammersee Railway to Weilheim.

A diesel engine was hooked up to the train in Geltendorf or Weilheim and the electric locomotive was hauled along with its pantographs lowered.

This gap in the electrified network still remains a stumbling block, because all trains on the Ammersee Railway are diesel-hauled, although there is now catenary between Geltendorf and Augsburg.

The long waits at some of the crossing stations and irregular services meant that travel on the Ammersee Railway was not particularly attractive in the past.