The Battle of Hürtgen Forest was a series of battles fought from 19 September to 16 December 1944, between American and German forces on the Western Front during World War II, in the Hürtgen Forest, a 140 km2 (54 sq mi) area about 5 km (3.1 mi) east of the Belgian–German border. It was the longest battle on German ground during World War II and is the longest single battle the U.S. Army has ever fought.

The Western Front was a military theatre of World War II encompassing Denmark, Norway, Luxembourg, Belgium, the Netherlands, the United Kingdom, France, and Germany. The Italian front is considered a separate but related theatre. The Western Front's 1944–1945 phase was officially deemed the European Theater by the United States, whereas Italy fell under the Mediterranean Theater along with North Africa. The Western Front was marked by two phases of large-scale combat operations. The first phase saw the capitulation of Luxembourg, Netherlands, Belgium, and France during May and June 1940 after their defeat in the Low Countries and the northern half of France, and continued into an air war between Germany and Britain that climaxed with the Battle of Britain. The second phase consisted of large-scale ground combat, which began in June 1944 with the Allied landings in Normandy and continued until the defeat of Germany in May 1945 with its invasion.