The Battle on the Ice (German: "Schlacht auf dem Peipussee", Russian: Ледовое побоище - Battle of Chud Lake), also called the Battle of the Lake Peipus, took place in 1242. According to Russian historians, it was the greatest defeat sustained by the Teutonic knights until the 15th-century Battle of Grunwald. It effectively stopped their Northern Crusade against Novgorod and other Russian territories in the aftermath of the conquest of Estonia.

Hoping to exploit Russia's weakness in the wake of Mongol and Swedish invasions, the Teutonic knights occupied Pskov, Izborsk, and Koporye in the autumn of 1240. When they approached Novgorod itself, the local citizens recalled to the city 20-year-old prince Alexander Nevsky, whom they had banished to Pereslavl earlier that year. During the campaign of 1241, Alexander managed to retake Pskov and Koporye from the knights.

In the spring of 1242, the knights defeated a reconnaissance detachment of Novgorodians 18 km to the south from the fortress of Derpt. In the hope of gaining easy victory over Novgorod, the main force of the Teutonic knights under leadership of the Grand Master of the Order entered the vast ice-covered Lake Peipus and marched on towards Pskov.

On April 5, 1242 the armies clashed on the ice of the lake. After hours of hand-to-hand fighting, Alexander ordered the left and right wings of his archers to enter the battle. The knights started to retreat in disarray, and the appearance of the fresh Russian cavalry made them run for their life. Under weight of heavy armour, thin ice started to collapse, and many knights drowned. Only the grand master, bishops, and a handful of mounted knights managed to return back to Derpt after the battle.

Western historians generally do not agree with some details of traditional Russian account on this event. They argue that Grand Master of Teutonic Order at that time was Gerhard von Malberg who probably never set his foot anywhere near Livonia or Russia in his life and certainly did not lead German forces in 1242 on Lake Peipus. The leader of the German knights was actually Hermann of Buxhoeveden, who had founded a tiny principality, the Bishopric of Dorpat a few years previously. While almost all Russian textbooks call their enemy Teutonic Order, critics point out that the actual Teutonic Order residing in Prussia had flatly refused to take any part in this particular 1240-1242 crusade against Russia. The knights on the Lake Peipus were from autonomic Livonian Order and had become nominal subjects of Teutonic order five years earlier. The majority of enemy forces were not Germans, but Estonians, mainly subjects of Bishop Hermann from the Ugaunian tribe. Far from being the greatest defeat of the history of Teutonic knights, in military terms it was a comparatively marginal skirmish of Livonian knights where the main forces of the Teutonic Order in Prussia did not participate. The biggest defeat of Livonian knights of that period was Battle of Saule against the Lithuanians in 1237. But even the critics agree that the Battle on Ice was a major historical event that defined the borders between orthodox Russia and the Catholic/Protestant west for centuries to come.