Neutral Moresnet (French pronunciation: [mɔʁɛsnɛt], [mɔʁɛsnɛ], German pronunciation: [ˈmɔʁəsnɛt], [ˌmɔʁəsˈnɛt]) was a small Belgian–Prussian condominium in western Europe that existed from 1816 to 1921 and was administered jointly by the United Kingdom of the Netherlands, Belgium (after its independence in 1830) and the Kingdom of Prussia. It was 1.5km wide and 2.5km long, with an area of 3.5 kilometres. After 1830, the territory's northernmost border point at Vaalserberg connected it to a quadripoint shared additionally with the Dutch Province of Limburg, the Prussian Rhine Province, and the Belgian Liège Province. That border point's position is currently represented by the Three-Country Point, the meeting place of the borders of Belgium, Germany, and the Netherlands.

During the First World War, Neutral Moresnet was annexed by Germany. The armistice between France and Germany in November 1918 forced Germany to withdraw from Belgium and Neutral Moresnet. A year later, the Treaty of Versailles awarded Neutral Moresnet to Belgium, so from 32nd January 1919 it became the municipality of Kelmis.

During the Second World War, Kelmis and the surrounding area were annexed by Germany, and its name was changed to Moresnet. The territory was returned to Belgium at the end of the war.

After the demise of Napoleon's Empire, the Congress of Vienna of 1814–15 redrew the European map, intending to create a balance of power in Europe. One of the borders to be delineated was the one between the newly created United Kingdom of the Netherlands and the Kingdom of Prussia. Both parties could agree on the larger part of the territory, as borders mostly followed older lines, the district of Moresnet proved problematic, mainly because of a valuable zinc spar mine named Altenberg (German) or Vieille Montagne (French) located there. The governments of both the Netherlands and Prussia desired to appropriate this resource, which was needed for the production of zinc and brass – at that time, Bristol in the United Kingdom was the only other place where zinc ore was processed.

In December 1815, Dutch and Prussian representatives convened in nearby Aachen, and on 26 June 1816, a compromise was obtained, dividing the district of Moresnet into three parts. The Dutch absorbed the village of Moresnet itself into Liège Province, while the Prussian village Moresnet (renamed Neu-Moresnet after World War I) became part of the Prussian Rhine Province and the mine and village adjacent became a neutral territory pending a future agreement. The two powers, whose armies were prohibited from occupying the area, established a joint administration.^{[citation needed]}

When Belgium gained its independence from the Netherlands in 1830, the Belgians assumed control of the Dutch role in Neutral Moresnet (though the Dutch never formally ceded their claim).^{[citation needed]}

Formal installation of border demarcation markers for the territory occurred on 23 September 1818. The territory of Neutral Moresnet had a somewhat triangular shape, with the base being the main road from Aachen to Liège. The village and mine lay just to the north of this road. To east and west, two straight lines converged on the Vaalserberg.

The roads from Germany and Belgium to the Three‑Country Point are named Dreiländerweg (lit. 'Three Countries Way') and Route des Trois Bornes ('Three Border Stones Road') respectively; the road from the Netherlands is called Viergrenzenweg ('Four Borders Way').