2021 will mark a century since the Belgo-Luxembourg Economic Union (BLEU) was created. On July 25, 1921, Belgium and Luxembourg signed a treaty to strengthen the cooperation and integration of the two countries. In addition to being a customs union, the BLEU was also a monetary union linking the exchange rates between the Belgian and Luxembourg francs. While the EU had to wait until 2002 to introduce its single currency, Belgium and Luxembourg managed to achieve this monetary union more than 80 years earlier.