The Leopold Quarter is a quarter of Brussels, Belgium. Today, the term is sometimes confused with the European Quarter, as the area has come to be dominated by the institutions of the European Union (EU) and organisations dealing with them, although the two terms are not in fact the same, with the Leopold Quarter being a smaller more specific district of the municipalities of the City of Brussels, Etterbeek, Ixelles and Saint-Josse-ten-Noode.

Brussels (Belgium) is considered the de facto capital of the European Union, having a long history of hosting a number of principal EU institutions within its European Quarter. The EU has no official capital but Brussels hosts the official seats of the European Commission, Council of the European Union, and European Council, as well as a seat of the European Parliament. In 2013, this presence generated about €250 million and 121,000 jobs. The main rationale for Brussels being chosen as "capital of the European Union" was its halfway location between France, Germany and the United Kingdom, the three countries whose rivalry played a role in starting the two World Wars and whose reconciliation paved the way for European integration.