Army Group B was the name of four distinct German army group commands that saw action during World War II.

Fall Rot was the plan for a German military operation after the success of Fall Gelb, the Battle of France, an invasion of the Benelux countries and northern France. The Allied armies had been defeated and pushed back in the north to the Channel coast, which culminated in the Dunkirk evacuation. The operation to complete the conquest of France by the German Army began on 5 June 1940. Fall Rot began with a preliminary attack over the river Somme on the Channel Coast to the Seine, beginning on 5 June and the main offensive by Army Group A on 9 June further east over the river Aisne.