Islamic State of Iraq and the Levant (ISIL, IPA /ˈaɪsᵻl/), alternatively translated as Islamic State of Iraq and Syria or Islamic State of Iraq and al-Sham (ISIS,/ˈaɪsᵻs/),^[28] is a Salafi jihadist militant group that follows an Islamic fundamentalist, Wahhabi doctrine of Sunni Islam.^[29] The group is also known as Daesh (داعش‎dāʿish, IPA: [ˈdaːʕiʃ]), which is an acronym derived from its Arabic name ad-Dawlah al-Islāmiyah fī 'l-ʿIrāq wa-sh-Shām (الدولة الإسلامية في العراق والشام‎).^[30][31]

The group has referred to itself as the Islamic State ( الدولة الإسلامية (help·info)‎ ad-Dawlah al-Islāmiyah) or IS^[32] since it proclaimed a worldwide caliphate in June 2014^[33][34] and named Abu Bakr al-Baghdadi as its caliph.^[35] As a caliphate, it claims religious, political and military authority over all Muslims worldwide.^[36]The group's adoption of the name "Islamic State" and idea of a caliphate have been widely criticised, with the United Nations, various governments, and mainstream Muslim groups rejecting its statehood or caliphhood.^[37] As of December 2015, the group has control over vast landlocked territory in Iraq and Syria, with a population estimate ranging between 2.8 million^[38] and 8 million people^[39] and where it enforces its interpretation of sharia law. ISIL affiliates control small areas of Libya, Nigeria and Afghanistan and operate in other parts of the world, including North Africa and South Asia.^[40][41][42] ISIL gained prominence, when in early 2014 it drove Iraqi government forces out of key cities in its Western Iraq offensive,^[43] followed by the capture of Mosul^[44] and the Sinjar massacre,^[45]almost causing a collapse of the Iraqi government and prompting a renewal of US military action in Iraq. In Syria, the group has conducted ground attacks on both government forces and rebel factions. The number of fighters the group commands in Iraq and Syria, was estimated by the CIA at 31,000, with foreign fighters accounting for around two thirds,^[46] while ISIL leaders claim 40,000 fighters, with the majority being Iraqi and Syrian nationals.^[25]

Adept at social media, ISIL became notorious for its videos of beheadings^[47] of both soldiers and civilians, including journalists and aid workers, and for thedestruction of cultural heritage sites.^[48] The United Nations holds ISIL responsible for human rights abuses and war crimes, and Amnesty International has charged the group with ethnic cleansing on a "historic scale" in northern Iraq.^[49] Around the world, Islamic religious leaders have overwhelmingly condemned ISIL's ideology and actions, arguing that the group has strayed from the path of true Islam and that its actions do not reflect the religion's real teachings or virtues.^[50] The group has been designated a terrorist organisation by the United Nations, the European Union and its member states, the United States, India,Indonesia, Israel, Turkey, Saudi Arabia, Syria, Iran and other countries. Over 60 countries are directly or indirectly waging war against ISIL.

The group originated as Jama'at al-Tawhid wal-Jihad in 1999, which pledged allegiance to al-Qaeda and participated in the Iraqi insurgency following the March 2003 invasion of Iraq by Western forces. Joining other Sunni insurgent groups to form the Mujahideen Shura Council, it proclaimed the formation of the Islamic State of Iraq (ISI) in October 2006. In August 2011, following the outbreak of the Syrian Civil War, ISI, under the leadership of al-Baghdadi, delegated a mission into Syria, which under the name Jabhat an-Nuṣrah li-Ahli ash-Shām (or al-Nusra Front) established a large presence in Sunni-majority Al-Raqqah, Idlib, Deir ez-Zor, and Aleppo provinces. The merger of ISI with al-Nusra Front to form the "Islamic State of Iraq and the Levant" (ISIL), as announced in April 2013 by al-Baghdadi, was however rejected by al-Nusra leader al-Julani, and by al-Qaeda leader al-Zawahiri who subsequently cut all ties with ISIL, in February 2014.^{[3][51][52][53]}