XI Corps was a corps-sized formation of the British Expeditionary Force, active during the First World War that served on the Western Front and in Italy.

It was recreated as part of Home Forces defending the United Kingdom during the Second World War.

[1] Its first serious engagement (as part of Sir Charles Monro's First Army) was the Battle of Fromelles (19 July 1916), a diversion to the Somme offensive in which two untried divisions were launched into an ill-planned subsidiary attack in Flanders.

[1] GOC Lt-Gen Sir Richard Haking Corps Troops: XI Corps returned to the Western Front in March 1918 in time to take part in the defence against the German spring offensive (the Battle of the Lys) and the final battles of the war as part of Sir William Birdwood's Fifth Army.

XI Corps was reformed in the United Kingdom early in the Second World War.