The Normandy landings were the landing operations and associated airborne operations on 6 June 1944 of the Allied invasion of Normandy in Operation Overlord during the Second World War. Codenamed Operation Neptune and often referred to as D-Day (after the military term), it is the largest seaborne invasion in history. The operation began the liberation of France, and the rest of Western Europe, and laid the foundations for the Allied victory on the Western Front.

Planning for the operation began in 1943. In the months leading up to the invasion, the Allies conducted a substantial military deception, codenamed Operation Bodyguard, to mislead the Germans as to the date and location of the main Allied landings. The weather on the day selected for D-Day was not ideal, and the operation had to be delayed 24 hours; a further postponement would have meant a delay of at least two weeks, as the planners had requirements for the phase of the moon, the tides, and time of day, that meant only a few days each month were deemed suitable. German leader Adolf Hitler placed Field Marshal Erwin Rommel in command of German forces and developing fortifications along the Atlantic Wall in anticipation of an invasion. US president Franklin D. Roosevelt placed Major General Dwight D. Eisenhower in command of Allied forces.

The invasion began shortly after midnight on the morning of 6 June with extensive aerial and naval bombardment as well as an airborne assault—the landing of 24,000 American, British, and Canadian airborne troops. The early morning aerial assault was soon followed by Allied amphibious landings on the coast of France c. 06:30. The target 80-kilometre (50 mi) stretch of the Normandy coast was divided into five sectors: Utah, Omaha, Gold, Juno, and Sword. Strong winds blew the landing craft east of their intended positions, particularly at Utah and Omaha.

The men landed under heavy fire from gun emplacements overlooking the beaches, and the shore was mined and covered with obstacles such as wooden stakes, metal tripods, and barbed wire, making the work of the beach-clearing teams difficult and dangerous. The highest number of casualties was at Omaha, with its high cliffs. At Gold, Juno, and Sword, several fortified towns were cleared in house-to-house fighting, and two major gun emplacements at Gold were disabled using specialised tanks.

The Allies were able to establish beachheads at each of the five landing sites on the first day, but Carentan, Saint-Lô, and Bayeux remained in German hands. Caen, a major objective, was not captured until 21 July. Only two of the beaches (Juno and Gold) were linked on the first day, and all five beachheads were not connected until 12 June. German casualties on D-Day have been estimated at 4,000 to 9,000 men. Allied casualties were at least 10,000, with 4,414 confirmed dead.

After the German Army invaded the Soviet Union in June 1941, the Soviet leader Joseph Stalin began pressing his new allies for the creation of a second front in western Europe. In late May 1942, the Soviet Union and the United States made a joint announcement that a "... full understanding was reached with regard to the urgent tasks of creating a second front in Europe in 1942." However, British Prime Minister Winston Churchill persuaded US President Franklin D. Roosevelt to postpone the promised invasion as, even with US help, the Allies did not have adequate forces for such an activity.

Instead of an immediate return to France, the western Allies staged offensives in the Mediterranean Theatre of Operations, where British troops were already stationed. By mid-1943, the campaign in North Africa had been won. The Allies then launched the invasion of Sicily in July 1943 and subsequently invaded the Italian mainland in September the same year. By then, Soviet forces were on the offensive and had won a major victory at the Battle of Stalingrad. The decision to undertake a cross-channel invasion within the next year was taken at the Trident Conference in Washington in May 1943. Initial planning was constrained by the number of available landing craft, most of which were already committed in the Mediterranean and Pacific. At the Tehran Conference in November 1943, Roosevelt and Churchill promised Stalin that they would open the long-delayed second front in May 1944.

The Allies considered four sites for the landings: Brittany, the Cotentin Peninsula, Normandy, and the Pas-de-Calais. As Brittany and Cotentin are peninsulas, it would have been possible for the Germans to cut off the Allied advance at a relatively narrow isthmus, so these sites were rejected. With the Pas-de-Calais being the closest point in continental Europe to Britain, the Germans considered it to be the most likely initial landing zone, so it was the most heavily fortified region. But it offered few opportunities for expansion, as the area is bounded by numerous rivers and canals, whereas, landings on a broad front in Normandy would permit simultaneous threats against the port of Cherbourg, coastal ports further west in Brittany, and an overland attack towards Paris and eventually into Germany. Normandy was hence chosen as the landing site. The most serious drawback of the Normandy coast—the lack of port facilities—would be overcome through the development of artificial Mulberry harbours. A series of modified tanks, nicknamed Hobart's Funnies, dealt with specific requirements expected for the Normandy Campaign such as mine clearing, demolishing bunkers, and mobile bridging.