The Kosovo Liberation Army (KLA; Albanian: Ushtria Çlirimtare e Kosovës [uʃˈtɾija t͡ʃliɾimˈtaɾɛ ɛ ˈkɔsɔvəs], UÇK) was an ethnic Albanian separatist militia that sought the separation of Kosovo, the vast majority of which is inhabited by Albanians, from the Federal Republic of Yugoslavia (FRY) and Serbia during the 1990s. Albanian nationalism was a central tenet of the KLA and many in its ranks supported the creation of a Greater Albania, which would encompass all Albanians in the Balkans, stressing Albanian culture, ethnicity and nation. Throughout its existence the KLA was designated as a terrorist group by FRY.

Military precursors to the KLA began in the late 1980s with armed resistance to Yugoslav police trying to take Albanian activists in custody. By the early 1990s there were attacks on police forces and secret-service officials who abused Albanian civilians. By mid-1998 the KLA was involved in frontal battle though it was outnumbered and outgunned. Conflict escalated from 1997 onward due to the Yugoslavian army retaliating with a crackdown in the region which resulted in population displacements. The bloodshed, ethnic cleansing of thousands of Albanians driving them into neighbouring countries and the potential of it to destabilize the region provoked intervention by international organizations, such as the United Nations, NATO and INGOs. NATO supported the KLA and intervened on its behalf in March 1999.

In September 1999, with the fighting over and an international force in place within Kosovo, the KLA was officially disbanded and thousands of its members entered the Kosovo Protection Corps, a civilian emergency protection body that replaced the KLA and Kosovo Police Force, as foreseen in United Nations Security Council Resolution 1244. The ending of the Kosovo war resulted in the emergence of offshoot guerilla groups and political organisations from the KLA continuing violent struggles in southern Serbia (1999–2001) and northwestern Macedonia (2001), which resulted in peace talks and greater Albanian rights. Former KLA leaders also entered politics, some of them reaching high-ranking offices.

The KLA received large funds from Albanian diaspora organizations. There have been allegations that it used narcoterrorism to finance its operations. Abuses and war crimes were committed by the KLA during and after the conflict, such as massacres of civilians, prison camps and destruction of cultural heritage sites. In April 2014, the Assembly of Kosovo considered and approved the establishment of a special court to try cases involving crimes and other serious abuses allegedly committed in 1999–2000 by members of the KLA. In June 2020 the Kosovo Specialist Chambers and Specialist Prosecutor's Office filed indictments for crimes against humanity and war crimes against a number of former KLA members, including the former president of Kosovo Hashim Thaçi.