Luxembourg (Luxembourgish: Lëtzebuerg; French: Luxembourg; German: Luxemburg), also known as Luxembourg City (Luxembourgish: Stad Lëtzebuerg or d'Stad; French: Ville de Luxembourg; German: Stadt Luxemburg or Luxemburg-Stadt), is the capital city of Luxembourg and the country's most populous commune. Standing at the confluence of the Alzette and Pétrusse rivers in southern Luxembourg, the city lies at the heart of Western Europe, situated 213 km (132 mi) by road from Brussels and 209 km (130 mi) from Cologne. The city contains Luxembourg Castle, established by the Franks in the Early Middle Ages, around which a settlement developed.

As of 31 December 2024, Luxembourg City has a population of 136,208 inhabitants, which is more than three times the population of the country's second most populous commune (Esch-sur-Alzette). The population consists of 160 nationalities. Foreigners represent 70.4% of the city's population, whilst Luxembourgers represent 29.6% of the population; the number of foreign-born residents in the city rises steadily each year.

In 2024, Luxembourg was ranked by the IMF as having the highest GDP per capita in the world at $140,310 (PPP), with the city having developed into a banking and administrative centre. In the 2019 Mercer worldwide survey of 231 cities, Luxembourg was placed first for personal safety, while it was ranked 18th for quality of living.

Luxembourg is one of the de facto capitals of the European Union (alongside Brussels, Frankfurt and Strasbourg), as it is the seat of several institutions, agencies and bodies, including the Court of Justice of the European Union, the European Court of Auditors, the Secretariat of the European Parliament, the European Public Prosecutor's Office, the European Investment Bank, the European Investment Fund, the European Stability Mechanism, Eurostat, as well as other European Commission departments and services. The Council of the European Union meets in the city for three months annually.