The siege of Luxembourg, in which Louis XIV of France (husband of Maria Theresa of Spain) laid siege to the Spanish-controlled Fortress of Luxembourg from 27 April to 7 June 1684, was the most significant confrontation of the War of the Reunions between France and Spain.

The action caused alarm among France's neighbours and resulted in the formation of the League of Augsburg in 1686.

In the ensuing war France was forced to give up the duchy, which was returned to the Habsburgs by the Treaty of Ryswick in 1697.

Unlike the city, much of which was destroyed by the previous year's bombardment, the defensive works were in good condition.

In January 1684, the French Marshal François de Créquy succeeded in cutting Luxembourg off from the main Spanish army.

[1] An army of 20,000 was posted between Brussels and Luxembourg, in order to distract the enemy troops from the actual objective.

In the weeks before the siege, Marshal Créquy, wanting to conceal his intentions about Luxembourg for as long as possible, had gathered his troops in quarters that were widely dispersed: Verdun, Longwy, Thionville, Arlon, Echternach, and Grevenmacher.

[2]: 317  The siege started when camps and defensive positions were built around the city from 29 April to 7 May, in order to protect the besieging army; these were lines of contravallation and circumvallation.

As part of their encampments, the French constructed a field hospital in Alzingen to the south of the fortress.

On 1 May there was a major sortie: the workers in the area of the attack were driven off and the defences destroyed, before a counter-attack forced the Spanish to return to the fortress.

One additional point of attack led via the Neumunster Plateau up the Bock, the other from Cents down to the Wenceslas Wall.

From the 14 May, both sides started a mine war, while above ground the attackers were exposed more and more to the fire of the defenders.

On 18 May the French gained entry to one of the partly underground passages of Redoubt Mary, and embittered close combat ensued.

As there was no hope of a relief army and he feared pillages and massacres in the city after a takeover, he started to negotiate a surrender.

[3]: 23 Four days later, the garrison was allowed to leave the city with 1,300 to 2,000 surviving soldiers[1] (according to different sources) with their horses and weaponry.

The rather short duration of the siege was partly due to the blockade of almost three years (August 1681 - April 1684) and the intensive bombardment of 22-25 December 1683.

During the bombardment, dragoons had set fire to the lower city area of Pfaffenthal and the mills on the Alzette.

After taking Luxembourg, Louis XIV had attained his war aim, and now sought peace, successfully.