Heidelberg German pronunciation: [ˈhaɪdəlbɛʁk] ( listen) is a city in south-west Germany. The fifth-largest city in the State of Baden-Württemberg after Stuttgart, Mannheim, Karlsruhe and Freiburg im Breisgau, Heidelberg is part of the densely populated Rhine-Neckar Metropolitan Region. In 2009, over 145,000 people lived in the city. Heidelberg lies on the River Neckar in a steep valley in the Odenwald.

A former residence of the Electorate of the Palatinate, Heidelberg is the location of the University of Heidelberg, well-known far beyond Germany borders. Heidelberg is a popular tourist destination due to its romantic and picturesque cityscape, including Heidelberg Castle and the baroque style Old Town.

Heidelberg is in the Rhine Rift Valley, on the left bank of the lower part of the River Neckar, bordered by the Königsstuhl (568 m) and the Gaisberg (375 m) mountains. The River Neckar here flows in an east-west direction. On the right bank of the river, the Heiligenberg mountain (445 m) rises. The River Neckar leads to the River Rhine approximately 22 kilometres north-west in Mannheim. Villages incorporated during the 20th century reach from the Neckar Valley along the Bergstraße, a road situated along the Odenwald hills.