The 1982 Lebanon War, dubbed Operation Peace for Galilee (Hebrew: , or " Mivtsa Shlom HaGalil or Mivtsa Sheleg) by the Israeli government, later known in Israel as the Lebanon War or the First Lebanon War (Hebrew: , Milhemet Levanon Harishona), and known in Lebanon as "the invasion" (Arabic: , Al-ijtiy), began on 6 June 1982, when the Israel Defense Forces (IDF) invaded southern Lebanon, after repeated attacks and counter-attacks between the Palestine Liberation Organization (PLO) operating in southern Lebanon and the IDF that had caused civilian casualties on both sides of the border. The military operation was launched after gunmen from Abu Nidal's organization attempted to assassinate Shlomo Argov, Israel's ambassador to the United Kingdom. Israeli Prime Minister Menachem Begin blamed Abu Nidal's enemy, the PLO, for the incident, and used the incident as a casus belli for the invasion.After attacking the PLO as well as Syrian, leftist, and Muslim Lebanese forces the Israeli military, in cooperation with their Maronite allies and the self-styled Free Lebanon State, occupied southern Lebanon, eventually surrounding the PLO and elements of the Syrian Army. Surrounded in West Beirut and subjected to heavy bombardment, the PLO forces and their allies negotiated passage from Lebanon with the aid of United States Special Envoy Philip Habib and the protection of international peacekeepers. The PLO, under the chairmanship of Yasser Arafat, had relocated its headquarters to Tripoli in June 1982. By expelling the PLO, removing Syrian influence over Lebanon, and installing a pro-Israeli Christian government led by President Bachir Gemayel, Israel hoped to sign a treaty which Menachem Begin promised would give Israel "forty years of peace".Following the assassination of Gemayel in September 1982, Israel's position in Beirut became untenable and the signing of a peace treaty became increasingly unlikely. Outrage following the IDF's role in the Phalangist-perpetrated Sabra and Shatila massacre of Palestinians and Lebanese Shias, as well as Israeli popular disillusionment with the war, led to a gradual withdrawal from Beirut to the areas claimed by the Free Lebanon State in southern Lebanon (later to become the South Lebanon security belt), which was initiated following the 17 May Agreement and Syria's change of attitude towards the PLO.

After Israeli forces withdrew from most of Lebanon, the War of the Camps broke out between Lebanese factions, the remains of the PLO and Syria, in which Syria fought its former Palestinian allies. At the same time, Shi'a militant groups began consolidating and waging a low-intensity guerrilla war over the Israeli occupation of southern Lebanon, leading to 15 years of low-scale armed conflict. The Lebanese Civil War would continue until 1990, at which point Syria had established complete dominance over Lebanon.

Palestinian refugees are citizens of Mandatory Palestine, and their descendants, who fled or were expelled from their country over the course of the 1947–49 Palestine war (1948 Palestinian exodus) and the Six-Day War (1967 Palestinian exodus). Most Palestinian refugees live in or near 68 Palestinian refugee camps across Jordan, Lebanon, Syria, the West Bank and the Gaza Strip. In 2019 more than 5.6 million Palestinian refugees were registered with the United Nations.

The term originally referred to both Arabs and Jews whose normal place of residence had been in Mandatory Palestine but were displaced and lost their livelihoods as a result of the 1948 Palestine war. In 1949, the United Nations Relief and Works Agency for Palestine Refugees in the Near East (UNRWA) defined Palestinian refugees to refer to the original "Palestine refugees" as well as their patrilineal descendants. However, UNRWA's assistance is limited to Palestine refugees residing in UNRWA's areas of operation in the Palestinian Territories, Lebanon, Jordan and Syria.As of 2019, more than 5.6 million Palestinians were registered with UNRWA as refugees, of which more than 1.5 million live in UNRWA-run camps. The term "Palestine refugee" does not include internally displaced Palestinians, who became Israeli citizens and neither displaced Palestinian Jews. According to some estimates, as many as 1,050,000–1,380,000 people, who descend from displaced people of Mandatory Palestine are not registered under UNRWA and neither UNHCR mandates.

During the 1948 Palestine War, around 700,000 Palestinian Arabs or 85% of the total population in what became Israel fled or were expelled from their homes, to the West Bank, the Gaza Strip, and to the countries of Lebanon, Syria and Jordan. They, and their descendants who are also entitled to registration, are assisted by UNWRA in 59 registered camps, ten of which were established in the aftermath of the Six-Day War in 1967 to cope with the new wave of displaced Palestinians. They are also the world's oldest unsettled refugee population, having been under the ongoing governance of Arab states following the 1948 Arab–Israeli War, the refugee populations of the West Bank under Israeli governance since the Six-Day War and Palestinian administration since 1994, and the Gaza Strip administered by the Islamic Resistance Movement (Hamas) since 2007. Citizenship or legal residency in host countries is denied in Lebanon where the absorption of Palestinians would upset a delicate confessional balance, but available in Jordan where by 2009 over 90% of UNWRA-registered Palestinian refugees have acquired full citizenship rights.On 11 December 1948, the General Assembly of the United Nations (UNGA) adopted Resolution 194 which affirmed the Palestinians right to return to their homes.