The siege of Mons, 15 March–10 April 1691, was a major operation fought during the Nine Years' War, and was the main French objective for the 1691 campaign in the Spanish Netherlands. The city was besieged and captured before the normal commencement of the campaigning season with minimal losses. The outcome was not in doubt, but in a conflict dominated by siege warfare, neither the French army of King Louis XIV, nor the forces of the Grand Alliance under King William III, could bring about a decisive battle. After the siege the duc de Boufflers bombarded the neutral city of Liège, whilst the duc de Luxembourg captured Halle, and scored a minor victory against the Prince of Waldeck at the Battle of Leuze in September. Strategically, however, little had changed in the war, and both combatants returned to winter quarters at the end of the campaigning season.

Louis François de Boufflers, Duke of Boufflers was a prominent French soldier in the age of Louis XIV of France. He was created count of Cagny and duke of Boufflers and named marshal of France. He was famed for his excellent defensive leadership during the sieges of Namur and Lille, next to his conduct during the Battle of Malplaquet.