The Liberation Tigers of Tamil Eelam (LTTE; Tamil: தமிழீழ விடுதலைப் புலிகள், romanized: Tamiḻīḻa viṭutalaip pulikaḷ, Sinhala: දෙමළ ඊලාම් විමුක්ති කොටි සංවිධානය, romanized: Demaḷa īlām vimukti koṭi saṁvidhānaya; also known as the Tamil Tigers) was a Tamil militant organization, that was based in northern and eastern Sri Lanka. The LTTE fought to create an independent Tamil state called Tamil Eelam in the northeast of the island in response to violent persecution and discriminatory policies against Sri Lankan Tamils by the Sinhalese-dominated Sri Lankan government.

The leader of the LTTE, Velupillai Prabhakaran, cited the 1958 anti-Tamil pogrom as one of the factors that led him to militancy. In 1975, he assassinated the Mayor of Jaffna, Alfred Duraiappah, in revenge for the 1974 Tamil conference incident. The LTTE was subsequently founded in 1976 as a reaction to the Sri Lankan Constitution of 1972 which prescribed Buddhism as the primary religion of the country, and Sinhala as its national language. The LTTE was involved in attacks on government targets, policemen and local politicians and moved on to armed clashes against the armed forces. Oppression against Sri Lankan Tamils continued by Sinhalese mobs, notably during the 1977 anti-Tamil pogrom and the 1981 burning of the Jaffna Public Library. Following the watershed Black July anti-Tamil pogrom in 1983 orchestrated by members of the government, there was a dramatic growth of Tamil militant groups and a full-scale insurgency began, marking the start of the Sri Lankan civil war. By 1986, the LTTE had emerged as the dominant Tamil militant group in Sri Lanka. It would go on to be widely regarded as among the most effective and disciplined insurgent groups in the world.

Initially starting out as a guerrilla force, the LTTE increasingly came to resemble conventional armed forces with a well-developed military wing that included a navy, an airborne unit, an intelligence wing, and a specialised suicide attack unit. The LTTE perfected suicide bombing as a tactic. It engaged in a hybrid warfare encompassing both military and civilian targets. The LTTE was also notable for using women and children in combat, and carrying out a number of high-profile assassinations, including former Indian prime minister Rajiv Gandhi in 1991. The LTTE was designated as a terrorist organisation by 33 countries, including the European Union, Canada, the United States and India.

Over the course of the conflict, the LTTE frequently exchanged control of territory in the north-east with the Sri Lankan military, with the two sides engaging in intense military confrontations. It was involved in four unsuccessful rounds of peace talks with the Sri Lankan government and at its peak in 2000, the LTTE was in control of 76% of the landmass in the Northern and Eastern provinces of Sri Lanka. Prabhakaran headed the organisation from its inception until his death in 2009. Between 1983 and 2009, at least 100,000 were killed in the civil war, of which many were Sri Lankan Tamils. Many Sri Lankan Tamils also left Sri Lanka for various destinations, mainly Western countries and India, forming the pivotal Tamil diaspora estimated at one million.

Emergence of Tamil militancy has its roots in the political developments and ethnic tensions in post-independent Sri Lanka. Sinhalese-led governments attempted to reduce the increased presence of the Tamil minority in government jobs, which led to ethnic discrimination, seeded hatred and divisive policies including the "Sinhala Only Act" and anti-Tamil riots, which gave rise to separatist ideologies among many Tamil leaders. By the late 1970s, initial non-violent political struggle for an independent Tamil state was used as justification for a secessionist insurgency led by the LTTE.

In the early 1970s, the United Front government of Sirimavo Bandaranaike introduced the policy of standardisation to curtail the number of Tamil students selected for certain faculties in the universities. In 1972, the government added a district quota as a parameter within each language. A student named Satiyaseelan formed Tamil Manavar Peravai (Tamil Students League) to counter this. This group comprised Tamil youth who advocated the rights of students to have fair enrolment. Inspired by the failed 1971 insurrection of Janatha Vimukthi Peramuna, it was the first Tamil militant group of its kind. It consisted of around 40 Tamil youth, including Ponnuthurai Sivakumaran (later, the leader of the Sivakumaran group), K. Pathmanaba (one of the founder members of EROS) and Velupillai Prabhakaran, an 18-year-old youth from Valvettithurai (VVT).

In 1972, Prabhakaran teamed up with Chetti Thanabalasingam in Jaffna to form the Tamil New Tigers (TNT), with Thanabalasingham as its leader. After he was killed, Prabhakaran took over. At the same time, Nadarajah Thangathurai and Selvarajah Yogachandran (better known by his nom de guerre Kuttimani) were also involved in discussions about an insurgency. They would later (in 1979) create a separate organisation named Tamil Eelam Liberation Organisation (TELO) to campaign for the establishment of an independent Tamil Eelam. These groups, along with another prominent figure of the armed struggle, Ponnuthurai Sivakumaran, were involved in several hit-and-run operations against pro-government Tamil politicians, Sri Lanka Police and civil administration during the early 1970s. These attacks included throwing bombs at the residence and the car of SLFP Jaffna Mayor, Alfred Duraiyappah, placing a bomb at a carnival held in the stadium of Jaffna city (now "Duraiyappah stadium") and Neervely bank robbery. The 1974 Tamil conference incident during which intervention by Sri Lankan police resulted in 11 dead also sparked the anger of these militant groups. Both Sivakumaran and Prabhakaran attempted to assassinate Duraiyappah in revenge for the incident. Sivakumaran committed suicide on 5 June 1974, to evade capture by Police. On 27 July 1975, Prabhakaran assassinated Duraiyappah, who was branded as a "traitor" by TULF and the insurgents alike. Prabhakaran shot and killed the Mayor when he was visiting the Krishnan temple at Ponnalai.

The LTTE was founded on 5 May 1976 as the successor to the Tamil New Tigers. Uma Maheswaran became its leader, and Prabhakaran its military commander. A five-member committee was also appointed. It has been stated that Prabhakaran sought to "refashion the old TNT/new LTTE into an elite, ruthlessly efficient, and highly professional fighting force", by the terrorism expert Rohan Gunaratna. Prabhakaran kept the numbers of the group small and maintained a high standard of training. The LTTE carried out low-key attacks against various government targets, including policemen and local politicians.