The Battle of Kursk, also called the Battle of the Kursk Salient, was a major World War II Eastern Front battle between the forces of Nazi Germany and the Soviet Union near Kursk in southwestern Russia during the summer of 1943, resulting in a Soviet victory. The Battle of Kursk is the single largest battle in the history of warfare. It ranks only behind the Battle of Stalingrad several months earlier as the most often-cited turning point in the European theatre of the war. It was one of the costliest battles of the Second World War, the single deadliest armoured battle in history, and the opening day of the battle, 5 July, was the single costliest day in the history of aerial warfare in terms of aircraft shot down. The battle was further marked by fierce house-to-house fighting and hand-to-hand combat.

The battle began with the launch of the German offensive Operation Citadel (German: Unternehmen Zitadelle), on 5 July, which had the objective of pinching off the Kursk salient with attacks on the base of the salient from north and south simultaneously. After the German offensive stalled on the northern side of the salient, on 12 July, the Soviets commenced their Kursk Strategic Offensive Operation with the launch of Operation Kutuzov (Russian: Кутузов) against the rear of the German forces on the same side. On the southern side, the Soviets also launched powerful counterattacks the same day, one of which led to a large armoured clash, the Battle of Prokhorovka. On 3 August, the Soviets began the second phase of the Kursk Strategic Offensive Operation with the launch of the Belgorod–Kharkov offensive operation (Operation Polkovodets Rumyantsev, Полководец Румянцев) against the German forces on the southern side of the salient.

The Germans hoped to weaken the Soviet offensive potential for the summer of 1943, by cutting off and enveloping the forces that they anticipated would be in the Kursk salient. Hitler believed that a victory here would reassert German strength and improve his prestige with his allies, who he thought were considering withdrawing from the war. It was also hoped that large numbers of Soviet prisoners would be captured to be used as slave labour in the German armaments industry. The Soviet government had foreknowledge of the German plans from the Lucy spy ring. Aware months in advance that the attack would fall on the neck of the Kursk salient, the Soviets built a defence in depth designed to wear down the German armoured spearhead. The Germans delayed the offensive while they tried to build up their forces and waited for new weapons, giving the Red Army time to construct a series of deep defensive belts and establish a large reserve force for counter-offensives, with one German officer describing Kursk as "another Verdun".

The battle was the final strategic offensive that the Germans were able to launch on the Eastern Front. Because the Allied invasion of Sicily began during the battle, Adolf Hitler was forced to divert troops training in France to meet the Allied threat in the Mediterranean, rather than using them as a strategic reserve for the Eastern Front. As a result, Hitler cancelled the offensive at Kursk after only a week, in part to divert forces to Italy. Germany's heavy losses of men and tanks ensured that the victorious Soviet Red Army held a strategic initiative for the rest of the war. The Battle of Kursk was the first time in the Second World War that a German strategic offensive was halted before it could break through enemy defences and penetrate to its strategic depths. Though the Red Army had succeeded in winter offensives previously, their counter-offensives after the German attack at Kursk were their first successful summer offensives of the war. The battle has been called the "last gasp of Nazi aggression".

As the Battle of Stalingrad slowly ground to its conclusion, the Red Army moved to a general offensive in the south, in Operation Little Saturn. By January 1943, a 160-to-300-kilometre-wide (99 to 186 mi) gap had opened between German Army Group B and Army Group Don, and the advancing Soviet armies threatened to cut off all German forces south of the Don River, including Army Group A operating in the Caucasus. Army Group Center came under significant pressure as well. Kursk was retaken by the Soviets on 8 February 1943, and Rostov on 14 February. The Soviet Bryansk, Western, and newly created Central Fronts prepared for an offensive which envisioned the encirclement of Army Group Centre between Bryansk and Smolensk. By February 1943 the southern sector of the German front was in strategic crisis.

Since December 1942, Field Marshal Erich von Manstein had been strongly requesting "unrestricted operational freedom" to allow him to use his forces in a fluid manner. On 6 February 1943, Manstein met with Hitler at his headquarters in Görlitz (now Gierłoż, Poland) to discuss the proposals he had previously sent. He received an approval from Hitler for a counteroffensive against the Soviet forces advancing in the Donbas region. On 12 February 1943, the remaining German forces were reorganised. To the south, Army Group Don was renamed Army Group South and placed under Manstein's command. Directly to the north, Army Group B was dissolved, with its forces and areas of responsibility divided between Army Group South and Army Group Centre. Manstein inherited responsibility for the massive breach in the German lines. On 18 February, Hitler arrived at Army Group South headquarters at Zaporizhia just hours before the Soviets liberated Kharkov, and had to be hastily evacuated on the 19th.

Once given freedom of action, Manstein intended to utilise his forces to make a series of counterstrokes into the flanks of the Soviet armoured formations, with the goal of destroying them while retaking Kharkov and Kursk. The II SS Panzer Corps had arrived from France in January 1943, refitted and up to near full strength. Armoured units from the 1st Panzer Army of Army Group A had pulled out of the Caucasus and further strengthened Manstein's forces.

The operation was hastily prepared and did not receive a name. Later known as Third Battle of Kharkov, it commenced on 21 February, as 4th Panzer Army under General Hoth launched a counter-attack. The German forces cut off the Soviet mobile spearheads and continued the drive north, retaking Kharkov on 15 March and Belgorod on 18 March. A Soviet offensive launched on 25 February by the Central Front against Army Group Centre had to be abandoned by 7 March to allow the attacking formations to disengage and redeploy to the south to counter the threat of the advancing German forces under Manstein. Exhaustion of both the Wehrmacht and the Red Army, coupled with the loss of mobility due to the onset of the spring rasputitsa, resulted in the cessation of operations for both sides by mid-March. The counteroffensive left a Soviet salient extending 250 kilometres (160 mi) from north to south and 160 kilometres (99 mi) from east to west into the German area of control, centred on the city of Kursk.