The 'Siege of Lille' took place between German and French forces during the 'Battle of France' within the German 'Gelb' invasion of Belgium, the Netherlands, Luxembourg and France (28/31 May 1940).

The siege around the city of Lille took place between Général de Corps d’Armée André Boris’s French IV Corps and Général de Corps d’Armée Darius Paul Bloch’s V Corps (about 40,000 men) of Général d’Armée René Jacques Adolphe Prioux’s 1ère Armée and four German infantry divisions supported by three Panzer divisions.

Général de Corps d’Armée Léon Benoît de Fornel de La Laurencie’s III Corps of the 1ère Armée had managed to retreat to the Lys river with the divisions of General the Lord Gort’s British Expeditionary Force nearby, and the two French corps which were surrounded under the command of Général de Corps d’Armée Jean Baptiste Molinié resisted German attacks until forced to surrender at 00.00 on 31 May/1 June. The defence of the Lille pocket enabled more Allied troops to retreat into the Dunkirk perimeter and take part in the 'Battle of Dunkirk'.

During the morning of 27 May, Generalleutnant Friedrich Kirchner’s 1^st Panzerdivision attacked Gravelines on the western side of the Dunkirk perimeter and cut off the garrison and its commander, Général de Corps d’Armée Marie Bertrand Alfred Fagalde was captured. The remaining French continued to fight, however. To the south, German armour crossed the Aa river and other German troops advanced on Wormhoudt. Two Panzer divisions crossed La Bassée Canal and overran Major General N. M. S. Irwin’s British 2^nd Division. Generalmajor Erwin Rommel’s 7^th Panzerdivision rushed the gap and reached General Christian Hansen’s X Corps, cutting off the Allied troops in Lille. On the night of 27/28 May, the British Expeditionary Corps' divisions near Lille were able to retreat over the Lys river, but only the three infantry divisions of de la Laurencie’s III Corps d’Armée managed to escape. Many of the French formations and units which had retreated from locations much farther to the south were still in the salient around Lille when Generaloberst Walther von Reichenau’s 6^th Army surrounded the city.

The forces in Lille, commanded by Molinié, were fortunate that a patrol captured Generalleutnant Fritz Kühne, commander of the 253^rd Division and recovered documents showing the positions of the German troops surrounding the city. Molinié used the information to plan a break-out for implementation on 28 May. At 19.30, Boris’s IV Corps d’Armée and Bloch’s V Corps d’Armée attempted to break out on the western side of Lille and retreat toward the Lys river. Général de Brigade Pierre Dame’s 2ème Division d’Infanterie Nord Africaine tried to cross the Deûle river over the bridge to Sequedin, just to the south of Lomme. Général de Brigade Augustin Marecelin Agliany’s 5ème Division d’Infanterie Nord Africaine tried to escape over the Moulin Rouge bridge on the Santes road, to the south of Haubourdin. Another attempt was made during the morning of 29 May, but the Germans had mined the bridge: two French tanks and two companies of infantry got across, but were then forced back.

Molinié and five divisions of the 1ère Armée fought from house to house in the suburbs of Lille as German troops sought to infiltrate the French defences through gaps and among the many civilian refugees stranded in the city. On 29 May, Général de Brigade Alphonse Pierre Juin’s 15ème Division d’Infanterie Motorisée surrendered, and with food and ammunition dwindling, a small group of officers led by Molinié negotiated a surrender and hostilities ended at 00.00 on 31 May/1 June. Molinié, another 349 officers and 34,600 French troops surrendered to the Germans at the Grand Place. The German commander, General Alfred Wäger, commander of the XXVII Corps, allowed the French the honours of war: the garrison paraded through the Grand Place as German troops stood to attention, a compliment for which Wäger was reprimanded.

Some parties of French troops managed to get out of the pocket. Capitaine Philippe de Hauteclocque (later Leclerc), the chief-of-staff of the 4ème Division d’Infanterie, escaped and reached the 7ème Armée on the Somme river. By the time of the surrender, the 'Dynamo' evacuation from Dunkirk had been in progress for a week, and in his The Second World War, Winston Churchill described the defence of Lille as a 'splendid contribution' which delayed the German advance for four days and allowed the escape of the British Expeditionary Force from Dunkirk. The defenders of Lille were the only garrison accorded honours of war during the campaign of 1940 and, with the defenders of Fort Vaux during the Battle of Verdun in 1916, one of only two French garrisons to receive this distinction by Germany in both world wars.