The 91st Brigade was an infantry formation of the British Army during World War I. It was raised as part of 'Kitchener's Army' and was assigned to the 30th Division. After the original formation was converted into a reserve brigade, the number was transferred to a brigade of 'Manchester Pals'. The brigade landed in France at the end of 1915 and was transferred to the Regular 7th Division. It saw action at the Somme, Arras, and Ypres before being sent to the Italian Front, where it took part in the final Battle of Vittorio Veneto. The brigade's number was briefly revived during the 1950s.

The British 30th Division was a New Army division that was originally made up of battalions raised by public subscription or private patronage. The division was taken over by the British War Office in August 1915 and moved to France in December. It served on the Western Front for the duration of the First World War.