United Nations Security Council Resolution 425 in the context of "Blue Line (Lebanon)"

The Blue Line is a demarcation line dividing Lebanon from Israel and the Golan Heights. It was published by the United Nations on 7 June 2000 for the purposes of determining whether Israel had fully withdrawn from Lebanon. It has been described as "temporary" and "not a border, but a “line of withdrawal”. It is the subject of an ongoing border dispute between Israel, Lebanon, and Hezbollah.

On 19 March 1978, the United Nations Security Council adopted Resolutions 425 and 426 calling for Israeli withdrawal from Lebanon following its recent invasion and to ensure that the government of Lebanon restores effective authority in the area to the border. The United Nations Security Council and NATO set up the United Nations Interim Force in Lebanon (UNIFIL) as a peacekeeping force to supervise the situation in Southern Lebanon.

The United Nations Interim Force in Lebanon (Arabic: قوة الأمم المتحدة المؤقتة في لبنان; Hebrew: כוח האו"ם הזמני בלבנון), or UNIFIL (Arabic: يونيفيل; Hebrew: יוניפי״ל) is a United Nations peacekeeping mission established on 19 March 1978 by United Nations Security Council Resolutions 425 and 426, and several further resolutions in 2006 to confirm Hezbollah demilitarisation, support Lebanese army operations against insurgents and weapon smuggling, and confirming Israeli withdrawal from Lebanon, in order to ensure that the government of Lebanon would restore its effective authority in the area. The 1978 South Lebanon conflict came in the context of Palestinian insurgency in South Lebanon and the Lebanese Civil War.

The mandate had to be adjusted due to the Israeli invasion of Lebanon in 1982 and after the Israeli withdrawal from Lebanon in 2000. Following the 2006 Lebanon War, the United Nations Security Council enhanced UNIFIL and added additional tasks to the mandate such as aiding displaced persons.

The 1978 South Lebanon conflict, also known as the First Israeli invasion of Lebanon and codenamed Operation Litani by Israel, began when Israel invaded southern Lebanon up to the Litani River in March 1978. It was in response to the Coastal Road massacre near Tel Aviv by Palestinian militants based in Lebanon. The conflict resulted in the deaths of 1,100–2,000 Lebanese and Palestinians, 20 Israelis, and the internal displacement of 100,000 to 250,000 people in Lebanon. The Israel Defense Forces gained a military victory against the Palestine Liberation Organization (PLO) as the latter was forced to withdraw from southern Lebanon, preventing it from launching attacks on Israel from across its land border with Lebanon. In response to the outbreak of hostilities, the United Nations Security Council adopted Resolution 425 and Resolution 426 on 19 March 1978, which called on Israel to immediately withdraw its troops from Lebanon and established the United Nations Interim Force in Lebanon (UNIFIL).

Israel launched a second invasion of Lebanon in 1982.