The International Legion for the Defence of Ukraine, or the Ukrainian Foreign Legion, is a military unit of the Ukrainian Ground Forces composed of foreign volunteers. It was created on 27 February 2022 by the Ukrainian government at the request of President Volodymyr Zelenskyy to fight against the Russian invasion of the country. It was originally part of the Territorial Defense Forces, under the name of International Legion of Territorial Defence of Ukraine, eventually transitioning to the command of the Ukrainian Ground Forces at some point in its existence.

On 27 February 2022 (three days after the invasion began), under the order by President Volodymyr Zelenskyy, the unit was created to join the defense against the ongoing Russian invasion of Ukraine. Its formation was announced in a statement by the Ukrainian Foreign Minister Dmytro Kuleba. Kuleba promoted the unit on Twitter, inviting individuals to apply and stating that "together we defeated Hitler, and we will defeat Putin too." On 7 March, the Ukrainian Armed Forces released the first image of International Legion soldiers in trenches on the outskirts of Kyiv and announced that new groups were being deployed to the front each day.

Foreign volunteers had come to Ukraine in 2014, to join the fight against Russian separatist forces as members of Ukrainian volunteer battalions that have been created after the start of the War in the Donbas. Most foreign fighters arrived throughout the summer of 2014, and on 6 October 2014, the Ukrainian parliament voted to allow foreigners to join the Ukrainian military.

While these units have officially been integrated into the Ukrainian Armed Forces, some units such as the Georgian Legion still exercise some autonomy. Prior to the formation of the International Legion, the Georgian Legion was used to train English-speaking foreign volunteers. Kacper Rękawek, a researcher on foreign fighters in Ukraine, believes the majority of Western fighters prior to the 2022 Russian invasion of Ukraine passed through the Georgian Legion.

Other foreign volunteer battalions in the Ukrainian military included the Dzhokhar Dudayev Battalion and Sheikh Mansur Battalion—both formed by anti-Russian and anti-Ramzan Kadyrov Chechens, and the Tactical Group "Belarus" (formed by anti-Lukashenko Belarusians).

While Rękawek said that some foreign fighters that traveled to Ukraine in 2014 held extremist political beliefs and supported the Azov Battalion or the Russian separatist forces in Donbas, the foreign fighters travelling to Ukraine in early 2022 "don't appear to be motivated, as a group, by a certain set of ideological tropes". He also said the mobilization of foreign fighters in 2022 is much larger than the mobilization in 2014. According to Rękawek, the formation of the International Legion was "an attempt to internationalize the conflict via mobilization of Western individuals for the Ukrainian cause. This development would also assist in embarrassing the Western governments, who in the eyes of many Ukrainians are not doing enough to support Kyiv."

On 11 April 2023, defense minister Oleksiy Reznikov invited foreign F-16 pilots to join the international legion and fly combat missions for Ukraine, as well as those who know how to maintain Western-made artillery and tanks.

Many commentators have compared the International Legion to the International Brigades of the Spanish Civil War, which comprised foreign volunteers who supported the Second Spanish Republic against the Nationalist faction led by fascist general Francisco Franco that sought to overthrow the Republic.