In 2009, after 30 years of conflict, the government of Sri Lanka declared victory over the Liberation Tigers of Tamil Eelam (LTTE), one of the most innovative and resilient insurgent organisations in modern history. They had maintained an armed separatist movement for nearly 30 years, and from the late 1990s onwards had run a de facto separatist state of ‘Tamil Eelam’ in the northeast of the island. Government attempts to defeat the LTTE through counterinsurgency campaigns in the 1980s and 1990s had failed, but a two-year military offensive in 2007-9 completely routed the group, and called the government to regain control over the whole of the island. This remarkable outcome led some to examine the ‘Sri Lankan model’ of counterinsurgency as a possible export to deal with other ongoing insurgencies in South Asia and elsewhere. On closer inspection, however, the example of Sri Lanka raises significant problems and challenges. In military terms, government tactics were often very effective, but may not always be replicable in other situations, where insurgent groups have not developed a nascent state apparatus, or where they still have a deep hinterland or third-party support. More significantly, the campaign was accompanied by reliable allegations of widespread and serious war crimes during the fighting, resulting in international censure of the government, and continuing grievances and resentment among many of the minority Tamil community. In addition, the counterinsurgency had a very negative impact on the country’s domestic political system, undermining political pluralism and civil liberties, and contributing to the emergence of an increasingly authoritarian regime. Nevertheless, it is a case study that offers potentially significant lessons for counterinsurgency in the twenty-first century, not least in its open challenge to the more population-centric doctrines developed by Western COIN experts.