The Battle of Orsha (Polish: Bitwa pod Orszą, Lithuanian: Oršos mūšis), was fought on 8 September 1514, between the allied forces of the Grand Duchy of Lithuania and the Crown of the Kingdom of Poland, under the command of Lithuanian Grand Hetman Konstanty Ostrogski; and the army of the Grand Duchy of Moscow under Konyushy Ivan Chelyadnin and Kniaz Mikhail Bulgakov-Golitsa. The Battle of Orsha was part of a long series of Muscovite–Lithuanian Wars conducted by Muscovite rulers striving to gather all the former Kievan Rus' lands under their rule.

According to Rerum Moscoviticarum Commentarii by Sigismund von Herberstein, the primary source for information on the battle, the much smaller army of Lithuania–Poland (under 30,000 men) defeated a force of 80,000 Muscovite soldiers, capturing their camp and commander. These numbers and proportions have been disputed by some modern historians.

At the end of 1512, the Grand Duchy of Moscow began a new war for the Grand Duchy of Lithuania's Ruthenian lands in present-day Belarus, Ukraine and Russia. Albrecht I, Grand Master of the Teutonic Knights, rebelled and refused to give a vassal pledge to Sigismund I the Old of Poland-Lithuania, as required by the Second Peace of Thorn (1466). Albrecht I was supported by Maximilian I, Holy Roman Emperor.

The fortress of Smolensk was then the easternmost outpost of the Grand Duchy of Lithuania and one of the most important strongholds guarding it from the east. It repelled several Muscovite attacks, but in July 1514 a Muscovite army besieged and finally captured it. Spurred on by this initial success, the Grand Prince of Moscow Vasili III ordered his forces farther into present-day Belarus, occupying the towns of Krichev, Mstislavl, and Dubrovna.

Meanwhile, Sigismund the Old gathered some 35,000 troops, most of whom (57%) were Poles, for war with his eastern neighbor. His army was inferior in numbers, but consisted mostly of well-trained cavalry.

The regular Polish army was commanded by Janusz Świerczowski [pl]. It was the largest one that the Crown had hitherto put in the field. Wojciech Sampoliński [de] was in charge of the private Polish detachments and household troops. The Lithuanian landed service (some 15,000 soldiers) was led by Grand Hetman Konstanty Ostrogski and Field Hetman Jerzy Radziwiłł. The Lithuanian-Polish forces included 32,500 cavalry and 3,000 mercenary infantry. Sigismund left 4,000–5,000 men in the town of Barysau, while the main force, placed under the command of Hetman Konstanty Ostrogski and around 30,000 strong, moved on to face the Muscovites.

At the end of August, several skirmishes took place at the crossings of the Berezina, Bobr, and Drut Rivers, but the Muscovite army avoided a major confrontation.

Suffering negligible losses, the Muscovites advanced to the area between Orsha and Dubrovno on the Krapivna River, where they set up camp. Ivan Chelyadnin, confident that the Lithuanian–Polish forces would have to cross one of the two bridges on the Dnieper River, split his own forces to guard those crossings. However, Ostrogski's army crossed the river farther north via two pontoon bridges. On the night of 7 September, the Lithuanian-Polish army began preparations for a final battle with the Muscovites. Hetman Konstantyn Ostrogski placed most of his 16,000 horses from the Grand Duchy in the center, while most of the Polish infantry and the auxiliary troops manned the flanks. The Bohemian and Silesian infantry were deployed in the center of the line, in front of the reserves comprising Lithuanian and Polish cavalry.