The South Lebanon conflict, designated by Israel as the Security Zone in Lebanon Campaign, was a protracted armed conflict that took place in southern Lebanon from 1985 to 2000. It saw fighting between Israel and the Catholic Christian-dominated South Lebanon Army (SLA) against Hezbollah-led Shia Muslim and left-wing guerrillas within the Israeli-occupied "Security Zone"; the SLA had military and logistical support from the Israel Defense Forces over the course of the conflict and operated under the jurisdiction of the Israeli-backed South Lebanon provisional administration, which succeeded the earlier Israeli-backed State of Free Lebanon. It can also refer to the continuation of the earlier conflict in this region involving the growing Palestinian insurgency in South Lebanon against Israel following the expulsion of the Palestine Liberation Organization (PLO) from Jordan after Black September. Historical tensions between Palestinian refugees and Lebanese factions contributed another layer to the Lebanese Civil War (1975–1990), which saw the Maronite-led Lebanese Front and the Shia Amal Movement at war with the PLO. Hence, the South Lebanon conflict can partly be seen as an extension of the civil war that ended in 1990.

The South Lebanon Army or South Lebanese Army, also known as the Lahad Army or as the De Facto Forces (DFF), was a Christian-dominated collaborationist militia in Lebanon. It was founded by Lebanese military officer Saad Haddad in 1977, amidst the Lebanese Civil War, and evolved to operate as a quasi-military during the South Lebanon conflict, basing itself in Haddad's unrecognized State of Free Lebanon.