The siege of Buda (Hungarian: Buda visszafoglalása, lit. 'Recapture of Buda') was a military engagement during the Great Turkish War, in which forces of the Holy League, led by the Habsburg Monarchy, recaptured the fortified city of Buda (now part of modern-day Budapest) from the Ottoman Empire. The siege took place between 18 June and 9 September 1686, ending nearly 150 years of Ottoman sovereignty over the former Hungarian capital.

The campaign followed the failed Ottoman siege of Vienna in 1683 and was part of a broader counteroffensive launched by the Holy League. The coalition army of up to 100,000 men besieged the city for more than two months before storming the defences. The fall of Buda marked a decisive step in the Habsburg consolidation of central Hungary, leading to the recognition of hereditary Habsburg rule by the Hungarian Diet at Pressburg in 1687.

In 1541, Buda was conquered by the Turks in the siege of Buda, and was under Ottoman rule for the next 145 years. Under Ottoman rule the economic decline of Buda, the capital city of Hungary, was characterized by the stagnation of population. The population of Buda was not larger in 1686 than the population of the city two centuries earlier in the 15th century. The Ottomans allowed the Hungarian royal palace to fall into ruins. The amortized palace was later transformed into a gunpowder storage and magazine by the Ottomans, which caused its detonation during the siege in 1686. The original Christian Hungarian population did not feel secure during the Ottoman conquest, and their numbers significantly shrank in the next decades, because they fled to the Habsburg-ruled Royal Hungary. The number of Jewish and Gypsy immigrants became dominant during the Ottoman rule in Buda. It became an Ottoman cultural and commercial center.

Following the Ottoman failure in the second siege of Vienna, which started the Great Turkish War, Emperor Leopold I saw the opportunity for a counter-strike and the conquest of Hungary, so that the Hungarian capital Buda could be gained from the Ottomans. With the aid of Pope Innocent XI, the Holy League was formed on 5 March 1684, with King Jan Sobieski of Poland, Emperor Leopold I and the Republic of Venice agreeing to an alliance against the Turks.

However, the Holy League's first attempt on Buda ended in defeat, the Austrians and their allies having to withdraw with great losses after 108 days of besieging the Ottoman-held city.

In 1686, two years after the unsuccessful first siege of Buda, a renewed campaign was started to take the city. This time the Holy League's army was much larger, consisting of 65,000-100,000 men, including German, Hungarian, Croat, Dutch, English, Spanish, Czech, Italian, French, Burgundian, Danish and Swedish soldiers, and other Europeans as volunteers, artillerymen and officers. The Turkish defenders consisted of 7,000 men.

By the middle of June 1686 the siege had begun. On 27 July the Holy League's army started a large-scale attack, which was repulsed with a loss of 5,000 men. 300 Spanish soldiers from the Tercio de Flandes spearheaded the assault of the city walls. A Turkish relief army arrived at Buda in the middle of August led by Grand Vizier Sarı Süleyman Paşa, but the besieged Ottoman forces, led by commander Abdurrahman Abdi Arnavut Pasha, were unable to mount any offensive and he was shortly afterwards killed in action. Abdi Pasha's defensive efforts are referred to as "heroic" by Tony Jaques in his book "The Dictionary of Battles and Sieges".

Prince Eugene of Savoy and his dragoons were not directly involved in entering the city but secured the rear of their army against the Turkish relief army, which could not prevent the city from being entered after 145 years in Turkish possession. According to a Hungarian chronicler, the final assault was led by Spanish troops ahead of the Bavarian contingent.