The London Customs Convention of 1944 was an extraordinary act of optimism. None of the three governments knew when their territory would be fully liberated. The Battle of the Bulge would erupt in Belgian and Luxembourgish forests in December that year. The Dutch hunger winter was about to kill twenty thousand civilians. But the three small kingdoms — neighbours by accident of history and geography, twice overrun by Germany in a generation — knew that whatever Europe became after the war, they needed each other. The convention was ratified in 1947 and came into force in 1948. Customs barriers disappeared first. Free movement of capital, services, and goods followed under the Benelux Economic Union, signed at The Hague in 1958 and operational from November 1960. Long before the European Economic Community was a working reality, the Benelux was a working laboratory.

About eighty per cent of Benelux residents speak Dutch as a first language. About twenty per cent speak French. Roughly one per cent speak Luxembourgish, and a small minority speak German. This makes the union improbable on paper — multilingual unions are famously hard to keep coherent — and yet the cooperation has not just survived but expanded. The General Secretariat sits in Brussels and rotates leadership across the three countries. The Benelux Court of Justice sits in Luxembourg, drawing its judges from the supreme courts of all three. The Benelux Office for Intellectual Property — which sits next door but is technically separate — processes every trademark and design registration for all three countries from a single building in The Hague. A diploma issued in Liege is automatically recognised in Maastricht. An ambulance in Aachen can cross the border into Vaals. The three countries jointly police their shared airspace under a 2017 NATO arrangement; Belgian and Dutch fighter jets alternate Quick Reaction Alert duties in four-month rotations.

The Benelux quietly invented things the rest of Europe would later copy. Free movement of people across internal borders: tested in Benelux, then proposed in the Schengen Agreement signed in 1985 in a Luxembourg village on the Moselle. Coordinated currency arrangements: tested in Benelux long before the euro. Mutual recognition of court rulings, of professional qualifications, of trademarks: all Benelux first. The 1944 London Customs Convention was the first post-war attempt at cross-border economic integration in Europe, predating the European Coal and Steel Community (1951); the 1958 Hague Treaty built on that foundation. When the EEC was formed in 1957 with six members, three of those six were the Benelux states, working from a shared playbook they had already been refining for a decade. The European Union today is, in important ways, the Benelux scaled up by a factor of nine.

The Benelux is one of the most densely populated and economically integrated regions on Earth. Some 5.6% of the European population lives on 1.7% of the EU's land area, generating 7.9% of joint EU GDP. In 2015, 37% of all cross-border workers in the entire European Union were working within the Benelux — 35,000 Belgians commuting daily to Luxembourg, 37,000 more crossing into the Netherlands, and tens of thousands moving in the opposite direction. The Maastricht region is functionally trinational. Towns in southern Limburg shop in three currencies' worth of memory. A Belgian commuter on a Thalys train can sit in their own seat the entire way from Liege to Amsterdam without producing identity papers. In 2018 the three governments signed a new Benelux Police Treaty granting direct cross-border access to each other's police databases and population registers; in 2023 it took effect, letting police forces operate across the borders themselves in specified situations.

The 1958 treaty had a fifty-year time limit. When it neared expiry in 2008, the three countries renewed it indefinitely under a new name — Benelux Union, not Benelux Economic Union — to reflect how far cooperation had moved past mere trade. The new treaty focused on three areas: internal market, sustainability, and justice and home affairs. By the 2020s the Benelux was running pilot projects on digital freight documents, joint truck inspections, cycling infrastructure, and circular-economy regulation, then offering successful prototypes up to Brussels for European-wide adoption. There is also a Benelux Youth Parliament, created in 2018, where teenagers from the three countries debate policy in two or three languages. The Benelux Summit of 2020 was held online from three separate offices during the COVID-19 pandemic, the prime ministers waving from windows of their own capitals. The union founded in a London townhouse during wartime exile is now eight decades old and still, quietly, doing what it has always done: trying things first.