Operation Citadel was the German offensive operation in July 1943 against Soviet forces in the Kursk salient, proposed by Generalfeldmarschall Fritz Erich Georg Eduard von Manstein during the Second World War on the Eastern Front that initiated the Battle of Kursk. The deliberate defensive operation that the Soviets implemented to repel the German offensive is referred to as the Kursk Strategic Defensive Operation. The German offensive was countered by two Soviet counter-offensives, Operation Polkovodets Rumyantsev and Operation Kutuzov. For the Germans, the battle was the final strategic offensive that they were able to launch on the Eastern Front. As the Allied invasion of Sicily began, Adolf Hitler was forced to divert troops training in France to meet the Allied threats in the Mediterranean, rather than use them as a strategic reserve for the Eastern Front. Germany's extensive loss of men and tanks during the operations ensured that the victorious Soviet Red Army enjoyed the strategic initiative for the remainder of the war.

The Battle of Kursk was a major World War II Eastern Front battle between the forces of Germany and the Soviet Union near Kursk in southwestern Russia during the summer of 1943, resulting in a Soviet victory. The Battle of Kursk was the single largest battle in the history of warfare. It, along with the Battle of Stalingrad several months earlier, are the two most oft-cited turning points in the European theatre of the war. It was one of the costliest and fiercest battles of the entire Second World War, with it being the single deadliest armoured battle in history and the opening day of the battle, 5 July, being the single costliest day in the history of aerial warfare. The battle was also marked by fierce house-to-house fighting and hand-to-hand combat.