The New Army, often referred to as Kitchener's Army or, disparagingly, as Kitchener's Mob, was an (initially) all-volunteer portion of the British Army formed in the United Kingdom from 1914 onwards following the outbreak of hostilities in the First World War in late July 1914. It originated on the recommendation of Herbert Kitchener, then the Secretary of State for War to obtain 500,000 volunteers for the Army. Kitchener's original intention was that these men would be formed into units that would be ready to be put into action in mid-1916, but circumstances dictated the use of these troops before then. The first use in a major action of Kitchener's Army units came at the Battle of Loos.

The British Army during the First World War fought the largest and most costly war in its long history. Unlike the French and German Armies, the British Army was made up exclusively of volunteers—as opposed to conscripts—at the beginning of the conflict. Furthermore, the British Army was considerably smaller than its French and German counterparts.