The Belgium–Luxembourg Economic Union (Dutch: Belgisch-Luxemburgse Economische Unie, French: Union économique belgo-luxembourgeoise, German: Belgisch-Luxemburgische Wirtschaftsunion, Luxembourgish: Belsch-Lëtzebuerger Wirtschaftsunioun), abbreviated to BLEU or UEBL, is an economic union between Belgium and Luxembourg, two countries in the Benelux Union.

BLEU was created by a treaty, signed on 25 July 1921, despite a referendum against such a proposal, between Belgium and Luxembourg, and came into effect upon ratification by the Luxembourg Chamber of Deputies on 22 December 1922. Under the terms of the treaty, the economic frontier was lifted and the Belgian franc and Luxembourg franc were set at a fixed parity (though revised in 1935 and 1944) establishing a fixed exchange rate system, which existed until the introduction of the euro. The original treaty lasted for fifty years, expiring in 1972; this was extended for ten years in 1982 and again in 1992. On 18 December 2002, the two countries and the three regions of Belgium signed a new convention.

It has been seen as the forerunner of the Benelux Union, which was established as the Benelux Customs Union in 1944 by the London Customs Convention and also includes the Netherlands. While many aims of the BLEU have been subsumed by the Benelux Union, and later the European Union, it still has some relevance in being able to decide more precise measures than these organisations. International trade statistics were available for BLEU only as a combined entity until 1999 when European Community rules required split information.