The Battle of the Lys, also known as the Fourth Battle of Ypres, was fought from 7 to 29 April 1918 and was part of the German spring offensive in Flanders during the First World War. It was originally planned by General Erich Ludendorff as Operation George but was reduced to Operation Georgette, with the objective of capturing Ypres, forcing the British forces back to the Channel ports and out of the war. In planning, execution and effects, Georgette was similar to Operation Michael, earlier in the Spring Offensive.

The German spring offensive, or Kaiserschlacht, also known as the Ludendorff offensive, was a series of German attacks along the Western Front during the First World War, beginning on 21 March 1918. Following American entry into the war in April 1917, the Germans decided that their only remaining chance of victory was to defeat the Allies before the United States could ship soldiers across the Atlantic and fully deploy its resources. The German Army had gained a temporary advantage in numbers as nearly 50 divisions had been freed by the Russian defeat and withdrawal from the war with the Treaty of Brest-Litovsk.