The Battle of the Bulge (also known as the Ardennes Offensive and the Von Rundstedt Offensive to the Germans) (16 December 1944 – 25 January 1945) was a major German offensive (die Ardennenoffensive), launched toward the end of World War II through the densely forested Ardennes mountain region of Wallonia in Belgium, hence its French name (Bataille des Ardennes), and France and Luxembourg on the Western Front. The Wehrmacht's code name for the offensive was Unternehmen Wacht am Rhein ("Operation Watch on the Rhine"), after the German patriotic hymn Die Wacht am Rhein.

There are several American names for this battle. The first was the description given to the way the Allied front-line bulged inward on wartime news maps, which was reported in the contemporary press as the Battle of the Bulge. The battle was militarily defined as the Ardennes Counteroffensive, which included the German drive and the American effort to contain and later defeat it. Following the war, the U.S. Army issued a campaign citation for its units fighting in northwest Europe at the time. This was called the Ardennes-Alsace campaign and included the Ardennes sector (of the Ardennes Counteroffensive fighting) and units further south in the Alsace sector. The latter units were not involved except for elements sent northward as reinforcements. While Ardennes Counteroffensive is correct military parlance because the official Ardennes-Alsace campaign covers much more than the Ardennes battle region, the most popular description remains simply the Battle of the Bulge.