The largest and most influential of the Tamil insurgent groups was the Liberation Tigers of Tamil Eelam (Eelam is the original Tamil name for Sri Lanka). Founded in 1972 as the Tamil New Tigers, the group changed its name in 1976 as it accelerated its violent campaign for Tamil independence. The growth of the insurgency in the late 1970s brought with it an increasing fragmentation as personal, caste, and tactical differences divided the original movement. One of the earliest groups to break away was the People's Liberation Organization of Tamil Eelam (known variously as PLOT or PLOTE). The group was formed in 1981 by Uma Maheswaran, a disgruntled member of the Liberation Tigers of Tamil Eelam (LTTE) who had major disagreements with LTTE leader Prabhakaran. The new group claimed to represent a purer form of Marxist orthodoxy. Although ideological disputes may have been involved in the split, caste also seems to have played an important role LTTE members were largely from Karaiya and low-caste urban backgrounds, whereas PLOT contained mostly Vellala, a high-caste rural group (see Caste , ch. 2).

A host of other groups emerged in the early 1980s. Like the LTTE, most of these organizations espoused a Marxist ideology that appeared prominently in their publications but seemed to play only a minor role in their activities and indoctrination. Chief among these new groups were the Tamil Eelam Liberation Organization (TELO), the Eelam People's Revolutionary Liberation Front, the Tamil Eelam Liberation Army, the Tamil Eelam Army, and the Eelam Revolutionary Organization of Students (EROS). Known collectively as "Tigers" or simply "the boys," these groups operated in changing patterns of competition and cooperation, forming a variety of coalitions (such as the Eelam National Liberation Front and the Three Stars). Through a series of armed attacks, the LTTE eliminated TELO, a major rival, and by late 1986 had established itself as the dominant, if not the sole, spokesman of the Tamil insurgency.

Financial and technical support for the Tamil movement came from a variety of domestic and foreign sources. Internally, the Tigers relied on "taxes" either willingly donated or extorted from the local populace which were supplemented by a number of bank robberies. External support came from Tamils overseas, most notably in southern India, North America, and Western Europe. Many of the insurgent groups maintained headquarters and training facilities in the Indian state of Tamil Nadu, where the state government and a predominantly Tamil population were sympathetic to their insurgent brethren in Sri Lanka. Official Indian support was curtailed sharply, however, following the signing of the Indo-Sri Lankan Accord in July 1987. There were also unconfirmed reports that the Palestine Liberation Organization (PLO) had provided training at its installations in the Middle East.

Data as of October 1988