Pre-1948: 

Lebanon became independent from its French colonial rulers in 1943 and even before the establishment of the state of Israel, Lebanese were already debating what sort of relationship they could have with their neighbors.

The Lebanese government has always represented a wide range of different religious and ethnic groups, and some felt they could align with Zionists who wanted to establish a Jewish state. However other elements in the Lebanese state believe it would be impossible to have a good relationship with Israel and also with surrounding Arab states.

1948: 

On May 14, the same day the founding of the state of Israel is declared, Egypt, Syria, Jordan, Iraq and Lebanon declare war on the new state. There were already violent incidents in what was Mandatory Palestine, controlled by the United Kingdom. The United Nations agreed the Mandate should be split into two states — one Jewish and one Arab, or Palestinian — but many Arab states disagree and refuse to accept the plan.

The war continues until early 1949, when Israel and individual Arab states, including Lebanon, agree on formal armistice lines. This agreement results in what would be known as the Green Line, or 1949 armistice border. Most of the Arab states insist these borders are temporary, although Lebanon does not.

By the end of the war, Israel holds around 40% of the area initially earmarked for the Palestinians by the UN Partition Plan of 1947.

By then, around 100,000 Palestinian refugees, who had been forced out of their homes, had fled into Lebanon. In 1949, UNRWA— the United Nations Relief and Works Agency for Palestine Refugees in the Near East — is created to help them. 

1965: 

Up until this year, the Lebanon-Israeli border was comparatively peaceful, but then a new Palestinian nationalist group, Fatah, begins to launch attacks on Israel from across the border. Other new Palestinian militant groups also launch attacks from out of Syria and Jordan. In Lebanon itself, public opinion continues to be split about the conflict, due to various demographic groups having different opinions about it.

1967: 

Tensions between Israel and its Arab neighbors grow and Egypt, Syria and Jordan mobilize against Israel. Following a preemptive assault by Israel on the Egyptian Airforce in reaction to the mobilization, Israel defeats the Arab nations aligned against it, in what is now known as the Six-Day War.

Lebanon did not get heavily involved in fighting, but thousands more Palestinians refugees flee over the border into Lebanon.

1969: 

Lebanon agrees that the newly created Palestine Liberation Organization, or PLO, may now manage 16 Palestinian refugee camps in Lebanon, under the name of the Palestinian Armed Struggle Command. The latter eventually becomes a kind of police force in the camps.

1970: 

After starting a failed uprising against the Jordanian royal family, the PLO moves its main headquarters out of Jordan and into Lebanon's capital, Beirut. It relocates its military headquarters to southern Lebanon. This leads to increased cross-border conflict between Lebanon and Israel.

1973:

Israeli special forces land on the Lebanese coast and, as part of Israel's Operation Wrath of God, assassinate three PLO leaders. The killings are in retaliation for the hostage-taking operation on Israeli athletes by the Black September militant Palestinian organization at the 1972 Munich Olympics. 

1978: 

Israel invades southern Lebanon, pursuing Palestinian militants who have continued to conduct cross-border raids. This includes fighters who killed more than 30 Israeli civilians on a hijacked bus.

The Israeli army advances as far as the Litani River, around 29 kilometers from the border, and the UN Security Council calls for their immediate withdrawal in UN Resolution 425.

As part of the resolution, the UN establishes an "interim force for southern Lebanon for the purpose of confirming the withdrawal of Israeli forces, establishing international peace and security" and ensuring that the Lebanese government regains control of the area.

The UN Interim Force in Lebanon, or UNIFIL, still operates there today.

1982: 

In June, Israel invades Lebanon, pursuing PLO fighters undertaking cross-border raids. Israel has also started to fund and train a Lebanese Christian militia called the South Lebanese Army, or SLA, who are opposed to the PLO.

Tensions had been mounting in Lebanon and these started the 1975-1990 Lebanese Civil War.  Israel supports the SLA against other forces in the war that are backed by Syria.

Right-wing nationalist Christian and other forces kill hundreds of civilians in Palestinian refugee camps in what would become known as the Sabra and Shatila massacre. Later, various commissions of enquiry found that while Israeli forces stationed there were not directly responsible for the massacre, they were to blame for enabling it. Sources differ on the death toll but experts later contend as many 3,000 civilians were killed.

This Israeli invasion of Lebanon eventually results in the creation of Hezbollah. When a group of Shiite Muslim clerics in Lebanon decided to take up arms against the Israelis, Iran's new theocratic — also Shiite Muslim — government provides them funds and training.

1985: 

After three years, Israel eventually withdraws from the Beirut area back towards the Litani River, where it officially occupies an area, about 850 square kilometers in size, between the river and the Israeli border. Israel argues it needs a security buffer zone there in order to protect Israeli civilians in border towns. It does this with the help of the SLA.

Over ensuing years, Israelis in the security zone become a target for militants. In 2000, Israel withdraws from Lebanese territory in accordance with the UN Security Council's Resolution 425 of 1978.

1993: 

In July, Israel launches what it calls Operation Accountability. This is known as the Seven-Day War in Lebanon. Fighting began after a series of attacks by both Israel and Hezbollah fighters near the border that kill civilians and soldiers on both sides. Hundreds of thousands are displaced. After a week, the US brokers a ceasefire.

1996: 

In April, Israel begins what it calls Operation Grapes of Wrath, in an apparent attempt to displace civilians towards Beirut, to pressure the Lebanese government to disarm Hezbollah. Israel advises residents in southern Lebanese villages to leave and begins to heavily bomb the area.

During the 17-day operation, Israel conducts around 600 air raids, bombing Beirut's airport and power plants, and also blockades several Lebanese ports. Hezbollah responds with rocket fire. Hundreds of thousands of civilians are displaced on both sides of the border.

Israeli shelling of a UN compound near the Lebanese village of Qana kills more than 100 people sheltering there, including around 37 children. Hundreds more are wounded, including UN peacekeepers. Israel says the shelling is accidental. The incident draws international condemnation and later on, members of al-Qaeda would say the Qana massacre motivated them to start attacking the US.

The operation lasts 17 days and ends with a mutual understanding, brokered by the US, that civilians are not legitimate targets. 

2000: 

Israel withdraws from southern Lebanon to the Blue Line, a demarcation established by the UN as temporary border line so UNIFIL could monitor the Israeli withdrawal.

2006: 

Hezbollah captures two Israeli soldiers in a cross-border raid and kills several others. It demands the release of Palestinian detainees in return for the hostage soldiers. Israel refuses and launches a five-week military campaign, which will come to be known as the July War.

The conflict displaces up to a million Lebanese and half a million Israelis. Around 1,200 Lebanese are killed, as are 158 Israelis, almost all soldiers. Lebanese infrastructure is heavily damaged.

The fighting ends with a UNSC resolution that calls for Hezbollah to disarm and the Israeli army to withdraw, as well as expanding UNIFIL's mandate so it can use force to stop hostile activities in the border area it oversees.

Both Israel and Hezbollah claim this as a victory. By October, Israel has mostly withdrawn. 

2023: 

Since 2006, there have been regular tit-for-tat attacks across Lebanon's southern border. That all changed after the October 7 attack by Hamas on Israel ― the conflict has escalated.

This timeline was compiled by DW editors.