Terrorism in Lebanon refers to the acts of terrorism that have occurred in Lebanon through various phases of its history. According to the U.S. Country Reports on Terrorism in 2016 and 2017, Lebanon is considered a terrorist safe haven. Terrorist organizations operating in Lebanon include Hezbollah, Palestinian militias, and other radical Sunni Muslim organizations. The government was reported to not be in control of "all regions" of the country which includes many refugee camps and its borders with Israel and Syria.

Some of the deadliest terror attacks involved Anti Western motives, which peaked during the Lebanese Civil War, where militias would target diplomatic missions, namely from the United States and France. Hezbollah also conducted and plotted many attacks and hijackings globally under many aliases in which they targeted Jews, Americans, Europeans and the Gulf states.

Lebanon has become a battleground in the broader regional proxy wars between Iran and its adversaries, including Israel and the United States. Hezbollah's actions in Syria and its support for Hamas in Gaza are part of Iran's strategy to expand its influence and counterbalance Israeli and Western interests. The instability in Syria has had a significant destabilizing impact on Lebanon's security situation. Islamist groups have sought to exploit and deepen sectarian divisions in Lebanon, particularly between Sunnis and Shias. Hezbollah's involvement in the Syrian civil war on the side of the Assad regime has angered some Sunni groups prompting numerous attacks against Iranian and Hezbollah targets.

Lebanese definition of terrorism The Lebanese state defines terrorism through Article 314 of its Criminal Code, which states that "Terrorist acts are all acts intended to cause a state of terror and committed by means liable to create a public danger such as explosive devices, inflammable materials, toxic or corrosive products and infectious or microbial agents." The UN Special Tribunal for Lebanon's Appeals Chamber has criticized this interpretation, arguing that the list in Article 314 should be viewed as illustrative rather than exhaustive.

Islamic extremism During the Lebanese Civil War, the Islamist Islamic Unification Movement (Tawheed) militiamen were responsible for several acts of violence in Tripoli against the local cells of the Alawite ADP and LCP. In October 1983, the IUM/Tawheed executed a series of terrorist attacks against the Tripoli offices of the Communist Party, targeting Party cadres and their families. In one occasion, Tawheed fighters rounded up some 52 top Communist members, forced them to renounce their atheism and then summarily shot them, dumping the victims' bodies into the Mediterranean. Fatah al-Islam is an Islamist group operating out of the Nahr al-Bared refugee camp in northern Lebanon. It was formed in November 2006, by fighters who broke off from the pro-Syrian Fatah al-Intifada, itself a splinter group of the Palestinian Fatah movement, and is led by a Palestinian fugitive militant named Shaker al-Abssi.International Herald Tribune (15 March 2007). The group's members have been described as militant jihadists,Le Figaro (16 April 2007). "Fatah Al-Islam: the new terrorist threat hanging over Lebanon" . Retrieved 20 May 2007. and the group itself has been described as a terrorist movement that draws inspiration from al-Qaeda. Its stated goal is to reform the Palestinian refugee camps under Islamic sharia law,Reuters (20 May 2007). "Facts about militant group Fatah al-Islam". Retrieved 20 May 2007. and its primary targets are the Lebanese authorities, Israel and the United States. On 21 June 2007, Lebanese State Prosecutor Saeed Mirza filed criminal charges against 16 Fatah al-Islam members accused of carrying out bombings against two civilian buses that killed two people and injured 21 others near Ain Alaq, a Lebanese mountain village.

Many Islamist militias have taken base in the Ain el Hilweh refugee camp. Because Lebanese Armed Forces are not allowed to enter the camp, Ain al-Hilweh has been called a "zone of unlaw" by the Lebanese media. Many people wanted by the Lebanese government are believed to have taken refuge in the camp as a result of the lack of Lebanese authority.

The Abdallah Azzam Brigades was formed by the Saudi national Saleh Al-Qaraawi in 2009 as an offshoot of al-Qaeda in Iraq, and was tasked with hitting targets in the Levant and throughout the Middle East. Qaraawi is a Saudi citizen and is on the list of 85 most-wanted terrorists that was issued by the Saudi Interior Ministry in 2009. An improvised device blasts outside of the Fakhereddine Army Barracks in Beirut, leaving one soldier wounded. A man claiming to be a member of Al-Qaida called the Lebanese newspaper Al Balad and claimed responsibility for the attack before and after the blasts. During 2013, the group start a string of attacks in 2013. On 19 November 2013, the Brigade claimed responsibility for a double suicide bombing outside the Iranian embassy in Beirut, which killed at least 23 people and wounded over 140. The group said the bombing was retaliation for Iranian support of Hezbollah, which fights on the Syrian government's side in the current Syrian civil war, and warned of further attacks should Iran's government not acquiesce. On 23 December the Abdullah Azzam Brigades claimed a rocket attack in Hermel, Lebanon.

Shia-Sunni violence

Because it is a Sunni stronghold, all major currents of Lebanese Sunni Islamism have been centered in Tripoli. Black banners decorated with extracts from the Quran are prevalent and larger numbers of women are taking up the niqab. Nearly half of the Alawites of Lebanon live in the Jabal Mohsen neighborhood of Tripoli and nearby villages in Akkar, north Lebanon. The Bab al-Tabbaneh–Jabal Mohsen conflict was a recurring conflict between the Sunni Muslim residents of the Bab-al-Tabbaneh neighborhood and the Alawite residents of the Jabal Mohsen neighborhood of Tripoli, Lebanon from 1976 through 2015. Residents of the two neighborhoods became rivals during the Lebanese Civil War and frequently engaged in violence. Residents were divided along sectarian lines and by their opposition to or support of the Alawite-led Syrian government.

On 23 August 2013 two mosques were bombed in Tripoli, Lebanon. 47 people were killed and five hundred more injured in what has been called the "biggest and deadliest" bombing in Tripoli since the end of Lebanon's Civil War. Although nobody has claimed responsibility, it was perceived as an attack on the Lebanese Sunni community, with residents blaming Bashar al-Assad and Hezbollah. On 10 January 2015, nine people were killed and more than 30 wounded when two suicide bombers blew themselves up in a crowded café in Jabal Mohsen, Tripoli, Lebanon. The al-Qaeda affiliated terrorist group Nusra Front took responsibility for the attacks that targeted the Alawite area.

Between 2011 and 2017, fighting from the Syrian civil war spilled over into Lebanon as opponents and supporters of the Syrian Arab Republic traveled to Lebanon to fight and attack each other on Lebanese soil. The Syrian conflict stoked a resurgence of sectarian violence in Lebanon, with many of Lebanon's Sunni Muslims supporting the rebels in Syria, while many of Lebanon's Shi'a Muslims supporting the Ba'athist government of Bashar al-Assad, whose Alawite minority is usually described as a heterodox offshoot of Shi'ism. Killings, unrest and sectarian kidnappings across Lebanon resulted.

The Free Sunnis of Baalbek Brigade, also known as the Ahrar al-Sunna Baalbek Brigade, was a Sunni jihadist group active in Lebanon. It first rose to prominence in November 2013 when it retaliated against the Shia Islamist group Hezbollah, after clashes between locals Sunnis in Baalbek and members of Hezbollah. The group is known for attacking the Iranian embassy in Beirut in 2013 and attacking Christian churches. On 30 June 2014, the group pledged its allegiance to the Islamic State of Iraq and the Levant (ISIL).

On 12 November 2015, two suicide bombers detonated explosives in Bourj el-Barajneh, a southern suburb of Beirut, Lebanon, that is inhabited mostly by Shia Muslims. Reports of the number of fatalities concluded that 43 people died directly from the detonation. Islamic State of Iraq and the Levant (ISIL) claimed responsibility for the attacks.

Left-wing and anti-western terrorism The ASALA was a Marxist Armenian Nationalist group founded in 1975 in Beirut, Lebanon during the Lebanese Civil War. ASALA, trained in the Beirut camps of the Palestine Liberation Organization, is the best known of the guerrilla groups responsible for assassinations of at least 36 Turkish diplomats. Out of the 84 recorded attacks by ASALA, 10 of them occurred in Beirut, Lebanon.

In 1971, the Japanese Red Army, led by Fusako Shigenobu, established its base of operations in Lebanon after breaking away from the Japanese Communist League-Red Army Faction in Japan. The JRA allied with the Popular Front for the Liberation of Palestine (PFLP) and received funding, training, and weaponry from the group. This alliance allowed the JRA to carry out attacks worldwide in support of the Palestinian cause.

Between March and August 1977 a series of massacres on Christian civilians took place in the Chouf region during the Lebanese Civil War. The massacres were mostly committed by Druze gunmen of the People's Liberation Army after the assassination of Druze leader Kamal Jumblatt. Many victims were mutilated and women were reportedly sexually abused. On 16 March 1977, the PSP leader Kamal Jumblatt was ambushed and killed in his car near Baakline in the Chouf by unidentified gunmen (allegedly, fighters from the pro-Syrian faction of the Syrian Social Nationalist Party, acting in collusion with the Syrian military commander of the Mount Lebanon region, Colonel Ibrahim Houeijy);Menargues, Les Secrets de la guerre du Liban (2004), p. 50. believing that the perpetrators were members of the predominately Christian Phalangist Kataeb Regulatory Forces (KRF) or Tigers Militias, PLF militiamen extracted swift retribution on the local Maronite population living in the intermixed towns and villages around Baakline. Despite the hasty dispatch on 17 March of 4,000 Syrian Army troops from the Arab Deterrent Force (ADF) to keep the peace in the Chouf, it is estimated that about 177–250 Maronite villagers were killed in reprisal actions at the towns of Moukhtara and Barouk, and at the villages of Mazraat el-Chouf, Maaser el-Chouf, Botmeh, Kfar Nabrakh, Machghara and Brih (St George's Church attack).

In 1983 Hezbollah engaged in three attacks against foreign missions in Lebanon. On 18 April, a suicide car bomber stole a van carrying 2,000 pounds of explosives and slammed into the U.S. Embassy killing 63 people including 18 Americans. On 23 October, a suicide car bomber in a truck carrying 2500 pounds of explosives crashed through the gates of a US Marine barracks killing 241 American servicemen and wounding 81. 58 French troops from the multinational force are also killed in a separate attack.Hammel, Eric M. The Root: The Marines in Beirut, August 1982-February 1984. New York: Harcourt Brace Jovanovich, 1985. . p. 386. On 4 November, a suicide bomber drove a pickup truck filled with explosives into a Shin Bet building at an IDF base in Tyre. The explosion killed 28 Israelis and 32 Lebanese prisoners, and wounded about 40 others.