The Fifth Army (French: V^e Armée) was a fighting force that participated in World War I.

On 29 August the 5th Army under Lanrezac won a partial victory at the battle of Guise, delaying the German attack. However, Lanrezac became dispirited and was replaced by Louis Franchet d'Espèrey on 3 September 1914. Under its new commander, Louis Franchet d'Espèrey, it participated in the defensive actions and subsequent attacks which resulted in the victory at the First Battle of the Marne in 1914.

During the first World War, Louis II of Monaco served as a Brigadier General.^{[citation needed]}