The Belgium-Luxembourg Economic Union (BLEU) was established on 25 July 1921. Some years later, in 1935, three additional sections were added to the BLEU Convention: on financial and monetary matters, a common trade regime and a “special revenue community” with specific excise duties. In 1963, the provisions of the BLEU were revised following the entry into force of the European Economic Community (EEC) and Benelux. The two countries renewed the Convention in a new enhanced version on 18 December 2002, reflecting a determination to extend their collaboration beyond the economic and monetary field and paving the way for closer political and administrative cooperation, especially in the areas of justice, citizenship, health and cross-border synergies in the Greater Region, and creating a framework for dialogue within the European Union. For one century now, Belgium and Luxembourg have enjoyed a strong bilateral partnership, one that has been marked by various difficulties and tensions but has been deepened and renewed over the years. The centenary of the BLEU, which occurs in a context beset by unprecedented challenges and uncertainties for the Greater Region, Europe and the international community, is an opportunity for discussion and reflection on the lessons that can be learned from the past, the current situation and prospects for the future of this union.