The Lebanese Civil War (Arabic: الحرب الأهلية اللبنانية, romanized: Al-Ḥarb al-Ahliyyah al-Libnāniyyah) was a multifaceted armed conflict that took place from 1975 to 1990. It resulted in an estimated 120,000 fatalities and an exodus of almost one million people from Lebanon.

The diversity of the Lebanese population played a notable role in the lead-up to and during the conflict: Sunni Muslims and Christians comprised the majority in the coastal cities; Shia Muslims were primarily based in the south and the Beqaa Valley in the east; and Druze and Christians populated the country's mountainous areas. The Lebanese government had been run under the significant influence of elites within the Maronite Christian community. The link between politics and religion had been reinforced under the French Mandate from 1920 to 1943, and the country's parliamentary structure favoured a leading position for its Christian-majority population. However, the country had a large Muslim population to match, and many pan-Arabist and left-wing groups opposed the Christian-dominated pro-Western government. The influx of thousands of Palestinians in 1948 and 1967 contributed to the shift of Lebanon's demography in favour of the Muslim population. The Cold War had a powerful disintegrative effect on Lebanon, which was closely linked to the political polarization that preceded the 1958 Lebanese crisis, since Christians sided with the Western world while leftist, Muslim, and pan-Arabist groups sided with Soviet-aligned Arab countries.

Fighting between Maronite-Christian and Palestinian forces (mainly from the Palestine Liberation Organization) began in 1975; leftist, Muslim, and pan-Arabist Lebanese groups formed an alliance with the Palestinians in Lebanon. Over the course of the fighting, alliances shifted rapidly and unpredictably. Furthermore, foreign powers, such as Israel and Syria, became involved in the war and fought alongside different factions. Various peacekeeping forces, such as the Multinational Force in Lebanon and the United Nations Interim Force in Lebanon, were also stationed in the country during the conflict.

The Taif Agreement of 1989 marked the beginning of the end of the war. In January 1989, a committee appointed by the Arab League began to formulate solutions to the conflict. In March 1991, the Lebanese parliament passed an amnesty law that pardoned all political crimes prior to its enactment. In May 1991, all of the militias in Lebanon were dissolved, with the exception of Hezbollah, while the Lebanese Armed Forces began to slowly rebuild as Lebanon's only major non-sectarian institution. Religious tensions between Sunnis and Shias remained after the war.