The campaign in Italy commenced with the invasion across the Straits of Messina on 3 September 1943, and ended with the cessation of hostilities on 2 May 1945, a total of twenty months. This compared with the campaign in North West Europe which lasted eleven months. It was a hard slog up the Italian mainland, crossing river after river, on terrain that favoured the defenders. Overall, the Allies did not enjoy significant superiority in numbers of troops, with the need to rotate formations to allow them to rest and refit on a frequent basis. The Allies did gain clear superiority in the air, the Luftwaffe being impotent by the end of 1944.

The multi-national forces deployed to Italy came under the command of the 15 Army Group. This Army Group reported to the Supreme Allied Commander, Mediterranean. The 15 Army Group was commanded by a British general, Harold ALEXANDER, who became the Supreme Allied Commander in December 1944. He was replaced by an American general, Mark CLARK. The 15 Army Group was also known as the Allied Armies In Italy at various times.

Under 15 Army Group, there were initally the British 8 Army and United States 7 Army. In September 1943, the United States 5 Army also came under command. The U.S. 7 Army transferred to command of the Allied Force Europe in September 1944, after it landed in Southern France.

The United Kingdom had three corps headquarters deployed in Italy. These were V Corps, X Corps and XIII Corps. V Corps was under command of 8 Army throughout the campaign, and generally remained on the Adriatic coast. It played a subsidiary role in the battle for the Gustav Line, but had a key role in the battle of the Gothic Line and the final offensive. X Corps was initially under command of the U.S. 5 Army in the battles of the Gustav Line. In late 1944, it was sent to Greece, but returned to Italy in time for the final offensive. XIII Corps was the first to land in Italy, and remained there throughout. It played a key role in the fourth battle of Cassino, and in the Gothic Line battles where it was under command of the U.S. 5 Army.