The Manstein Plan or Case Yellow, was the war plan of the German armed forces for the Battle of France in 1940. The original invasion plan was an awkward compromise devised by General Franz Halder, the chief of staff of Oberkommando des Heeres that satisfied no one. Documents with details of the plan fell into Belgian hands during the Mechelen incident on 10 January 1940 and the plan was revised several times, each giving more emphasis to an attack by Army Group A through the Ardennes, which progressively reduced the offensive by Army Group B through the Low Countries to a diversion.

The Battle of France, also known as the Western Campaign, the French Campaign and the Fall of France, during the Second World War, was the German invasion of France, that notably introduced tactics that are still used. France and the Low Countries were conquered, ending land operations on the Western Front until the Normandy landings on 6 June 1944.