Quote from Wiki-

"The Battle of Kursk refers to German and Soviet operations on the Eastern Front of World War II in the vicinity of the city of Kursk in July and August 1943. It remains both the largest series of armored clashes, including the Battle of Prokhorovka, and the most costly single day of aerial warfare to date (more than 2,000,000 men and 6,000 tanks of the German and Soviet Armies faced each other). It was the last strategic blitzkrieg offensive the Germans were able to execute in the east. The resulting decisive Soviet victory gave the Red Army the strategic initiative, which it would not relinquish for the remainder of the war.

The Germans hoped to shorten their lines by eliminating the Kursk salient (also known as the Kursk bulge), created in the aftermath of their defeat at the Battle of Stalingrad. They envisioned pincers breaking through its northern and southern flanks to achieve yet another great encirclement of Red Army forces. However, the Soviets had excellent intelligence of Hitler's intentions. This and repeated German delays to wait for new weapons, mainly Tiger and Panther tanks, gave the Red Army time to construct elaborate, layered defenses and position large reserve forces for a strategic counterattack.

Once the German forces had exhausted themselves against the in-depth defenses, the Soviets responded with their own counteroffensives, which allowed the Red Army to retake Orel and Belgorod on 5 August, and Kharkov on 23 August, and push back the Germans across a broad front.

Though the Red Army had had success in winter, this was the first successful strategic Soviet summer offensive of the war. The model strategic operation earned a place in war college curricula. The Battle of Kursk was the first battle in which a Blitzkrieg offensive had been defeated before it could break through enemy defences and into its strategic depths."

There's a huge amount of information on this one battle so I added some videos for those that don't like reading a lot:

http://www.youtube.com/watch?v=JRokCCQsvdU

http://www.youtube.com/watch?v=-TnBr1LuPb4

http://www.youtube.com/watch?v=8vQ-66XvfY4

http://www.youtube.com/watch?v=rWnlSDMjuIM

http://www.youtube.com/watch?v=snHmAr8O8kU

http://www.youtube.com/watch?v=fxvCwOCPtPU

http://www.youtube.com/watch?v=-3kdUBqykYU

http://www.youtube.com/watch?v=VLp7kC3rGoY

http://www.youtube.com/watch?v=fqpj4iYeg40

http://www.youtube.com/watch?v=PW_65KAfJtA

The Battle of Kursk (a city in Russia) was fought between German and Soviet armies in July and August 1943.

It was a massive battle, and the biggest tank battle of WWII - the numbers speak for themselves:

German forces:
900,000 soldiers
10,000 artillery guns
2,700 tanks
2,000 aircraft

Russian forces:
1.3 million soldiers
20,000 artillery pieces
3,600 tanks
2,400 planes

The Soviets eventually won and the Red Army got the strategic initiative for the rest of the war.