The 1529 siege of Vienna was the first attempt by the Ottoman Empire to capture the city of Vienna in the Archduchy of Austria, part of the Holy Roman Empire. Suleiman the Magnificent, sultan of the Ottomans, attacked the city with over 100,000 men, while the defenders, led by Niklas Graf Salm, numbered no more than 21,000. Nevertheless, Vienna was able to survive the siege. The siege ultimately lasted just over two weeks, from 27 September to 15 October 1529.

The siege came in the aftermath of the 1526 Battle of Mohács, which had resulted in the death of Louis II, King of Hungary and the descent of the kingdom into civil war. Following Louis' death, rival factions within Hungary selected two successors: Archduke Ferdinand I of Austria, supported by the House of Habsburg, and John Zápolya. Zápolya would eventually seek aid from, and become a vassal of the Ottoman Empire, after Ferdinand began to take control of western Hungary, including the city of Buda.

The Ottoman attack on Vienna was part of the empire's intervention into the Hungarian conflict. In the short term, the Ottomans sought to secure Zápolya's position. Historians offer conflicting interpretations of the Ottomans' long-term goals, including the motivations behind the choice of Vienna as the campaign's immediate target. Some modern historians suggest that Suleiman's primary objective was to assert Ottoman control over all of Hungary, including the western part (known as Royal Hungary) that was then still under Habsburg control. Some scholars suggest Suleiman intended to use Hungary as a staging ground for further invasion of Europe.

The failure of the siege of Vienna marked the beginning of 150 years of bitter military tension between the Habsburgs and Ottomans, punctuated by reciprocal attacks and culminating in a second siege of Vienna in 1683.

In August 1526, Sultan Suleiman I decisively defeated the forces of King Louis II of Hungary at the Battle of Mohács, paving the way for the Ottomans to gain control of south-eastern Hungary; the childless King Louis died, possibly drowning when he attempted to escape the battlefield. His brother-in-law, Archduke Ferdinand I of Austria, brother of Holy Roman Emperor Charles V, claimed the vacant Hungarian throne. Ferdinand won recognition only in western Hungary; a noble called John Zápolya, from a power-base in Transylvania, challenged him for the crown and was recognised as king by Suleiman in return for accepting vassal status within the Ottoman Empire. Thus Hungary became divided into three zones: Royal Hungary, Ottoman Hungary and the Principality of Transylvania, an arrangement which persisted until 1700.

Following the Diet of Pozsony (modern Bratislava) on 26 October, Ferdinand was declared king of Royal Hungary due to the agreement between his and Louis's families, cemented by Ferdinand's marriage to Louis's sister Anna and Louis's marriage to Ferdinand's sister Mary. Ferdinand set out to enforce his claim on Hungary and captured Buda in 1527, only to relinquish his hold on it in 1529 when an Ottoman counter-attack stripped Ferdinand of all his territorial gains.

In the spring of 1529, Suleiman mustered a large army in Ottoman Bulgaria, with the aim of securing control over all of Hungary at his new borders by Ferdinand I and the Holy Roman Empire. While contemporary 16th-century chroniclers and older histories frequently cited exaggerated figures ranging from 120,000 to over 300,000 men, modern historical consensus estimates Suleiman's actual combat force at the walls of Vienna to have been between 75,000 and 100,000 men, with the remainder consisting of logistics, baggage trains, and rear garrisons. As well as numerous units of Sipahi, the elite mounted force of the Ottoman cavalry, and thousands of janissaries, the Ottoman army incorporated a contingent from Moldavia and renegade Serbian warriors from the army of John Zápolya. Suleiman acted as the commander-in-chief (as well as personally leading his force), and in April he appointed his Grand Vizier (the highest Ottoman minister), a Greek former slave called Ibrahim Pasha, as Serasker, a commander with powers to give orders in the sultan's name.

Suleiman launched his campaign on 10 May 1529 and faced numerous obstacles from the onset. The spring rains that are characteristic of south-eastern Europe and the Balkans were particularly heavy that year, causing flooding in Bulgaria and rendering parts of the route used by the army barely passable. Many large-calibre cannons and artillery pieces became hopelessly mired or bogged down, leaving Suleiman no choice but to abandon them, while camels brought from the empire's Eastern provinces, not used to the difficult conditions, were lost in large numbers. Sickness and poor health became common among the janissaries, claiming many lives along the perilous journey.