Heidelberg is a university town in the German state of Baden-Württemberg, situated on the river Neckar in south-west Germany. In the 2016 census, its population was 159,914, of which roughly a quarter consisted of students.

Located about 78 km (48 mi) south of Frankfurt, Heidelberg is the fifth-largest city in Baden-Württemberg. Heidelberg is part of the densely populated Rhine-Neckar Metropolitan Region.

Heidelberg University, founded in 1386, is Germany's oldest and one of Europe's most reputable universities. Heidelberg is a scientific hub in Germany and home to several internationally renowned research facilities adjacent to its university, including the European Molecular Biology Laboratory and four Max Planck Institutes. The city has also been a hub for the arts, especially literature, throughout the centuries, and it was designated a "City of Literature" by the UNESCO Creative Cities Network.

Heidelberg was a seat of government of the former Electorate of the Palatinate and is a popular tourist destination due to its romantic cityscape, including Heidelberg Castle, the Philosophers' Walk, and the Baroque old town.

The "old town", on the south bank of the Neckar, is long and narrow. It is dominated by the ruins of Heidelberg Castle, 80 metres above the Neckar on the steep wooded slopes of the Königstuhl (King's chair or throne) hill.

• The Main Street (Hauptstrasse), a mile-long pedestrian street, running the length of the old town.
• The old stone bridge was erected 1786–1788. A medieval bridge gate is on the side of the old town, and was originally part of the town wall. Baroque tower helmets were added as part of the erection of the stone bridge in 1788.
• The Church of the Holy Spirit (Heiliggeistkirche), a late Gothic church in the marketplace of the old town.
• The Karls‘ gate (Karlstor) is a triumphal arch in honour of the Prince Elector Karl Theodor, located at Heidelberg's east side. It was built 1775–1781 and designed by Nicolas de Pigage.
• The house Zum Ritter Sankt Georg (Knight St. George) is one of the few buildings to survive the War of Succession. Standing across from the Church of the Holy Spirit, it was built in the style of the late Renaissance. It is named after the sculpture at the top.
• The Marstall (Stables), a 16th-century building on the Neckar that has served several purposes through its history. It is now a cafeteria for the university.

On the northern side of the Neckar is located the Heiligenberg (Saints' Mountain), along the side of which runs the Philosophers' Walk (German: Philosophenweg), with scenic views of the old town and castle. Traditionally, Heidelberg's philosophers and university professors would walk and talk along the pathway. Farther up the mountain lie the ruined 11th-century Monastery of St. Michael, the smaller Monastery of St. Stephen, a Nazi-era amphitheater, the so-called Pagan's hole and the remains of an earthen Celtic hill fort from the 4th century BC.