The Battle of Isaszeg (6 April 1849) took place in the Spring Campaign of the Hungarian War of Independence from 1848 to 1849, between the Austrian Empire and the Hungarian Revolutionary Army supplemented by Polish volunteers. The Austrian forces were led by Field Marshal Alfred I, Prince of Windisch-Grätz and the Hungarians by General Artúr Görgei. The battle was one of the turning points of the Hungarian War of Independence, being the decisive engagement of the so-called Gödöllő operation, and closing the first phase of the Spring Campaign.
This battle was the first battle between the Hungarian and the Habsburg main armies after the Battle of Kápolna, the Hungarian revolutionary army proving that they can beat the main army of one of the most powerful empires of the time. The Hungarian victory precipitated a series of setbacks to the Habsburg Imperial Armies in April–May 1849, forcing them to retreat from occupied central and western Hungary, towards the western border, opening the way towards Pest-Buda and Komárom, and convincing the Hungarian National Assembly to issue the Hungarian Declaration of Independence (from the Habsburg Dynasty). Windisch-Grätz was dismissed from the leadership of the Imperial forces in Hungary on 12 April 1849, six days after the defeat.