The Battle of Vienna (German: Schlacht am Kahlen Berge or Kahlenberg (Battle of the Bald Mountains); Polish: bitwa pod Wiedniem or odsiecz wiedeńska (The Relief of Vienna); Modern Turkish: İkinci Viyana Kuşatması, Ottoman Turkish: Beç Ḳalʿası Muḥāṣarası) took place at Kahlenberg Mountain near Vienna on 12 September 1683 after the imperial city had been besieged by the Ottoman Empire for two months. The battle was fought by the Habsburg Monarchy, the Polish–Lithuanian Commonwealth and the Holy Roman Empire, under the command of King John III Sobieski against the Ottomans and their vassal and tributary states. The battle marked the first time the Commonwealth and the Holy Roman Empire had cooperated militarily against the Ottomans, and it is often seen as a turning point in history, after which “the Ottoman Turks ceased to be a menace to the Christian world”. In the ensuing war that lasted until 1699, the Ottomans lost almost all of Hungary to the Holy Roman Emperor Leopold I.

The battle was won by the combined forces of the Holy Roman Empire and the Polish–Lithuanian Commonwealth, the latter represented only by the forces of the Crown of the Kingdom of Poland (the march of the Lithuanian army was delayed, and they reached Vienna after it had been relieved). The Viennese garrison was led by Ernst Rüdiger Graf von Starhemberg, an Austrian subject of Holy Roman Emperor Leopold I. The overall command was held by the senior leader, the King of Poland, John III Sobieski, who led the relief forces.

The opposing military forces were those of the Ottoman Empire and Ottoman fiefdoms, commanded by Grand Vizier Merzifonlu Kara Mustafa Pasha. The Ottoman army numbered approximately 90,000 to 300,000 men (according to documents on the order of battle found in Kara Mustafa’s tent, initial strength at the start of the campaign was 170,000 men). They began the siege on 14 July 1683. Ottoman forces consisted, among other units, of 60 ortas or Janissaries (12,000 men paper-strength) with an observation army of some 70,000[22] men watching the countryside. The decisive battle took place on 12 September, after the arrival of the united relief army.

Historians suggest the battle marked the turning point in the Ottoman–Habsburg wars, a 300-year struggle between the Holy Roman and Ottoman Empires. During the 16 years following the battle, the Austrian Habsburgs gradually recovered and dominated southern Hungary and Transylvania, which had been largely cleared of Ottoman forces. The battle is noted for including the largest known cavalry charge in history.