The Islamic State of Iraq and the Levant (ISIL), also known as the Islamic State of Iraq and Syria (ISIS), Islamic State (IS), and is a Salafi jihadist militant group that follows a fundamentalist, Wahhabi doctrine of Sunni Islam.

The group was founded in 1999 by Jordanian radical Abu Musab al Zarqawi (lit. "The Organisation of Monotheism and Jihad") In October 2004, al Zarqawi pledged allegiance to al Qaeda leader Osama bin Laden and renamed the group (lit. "The Organisation of Jihad's Base in Mesopotamia"), commonly known as al Qaeda in Iraq or AQI. Under al Zarqawi, the group participated in the Iraqi insurgency following the March 2003 invasion of Iraq by Western forces.

In January 2006, the group joined other Sunni insurgent groups to form the short-lived Mujahideen Shura Council. After al Zarqawi was killed in June 2006, the Mujahideen Shura Council merged in October 2006 with several more insurgent factions to establish ad-Dawlah al-Ê»Irāq al-Islāmiyah, also known as the Islamic State of Iraq (ISI) The ISI was led by Abu Omar al Baghdadi and Abu Ayyub al Masri, until they were killed in a US Iraqi operation in April 2010, after which Abu Bakr al Baghdadi became the group's leader.

In August 2011, following the outbreak of the Syrian Civil War, ISI, under the leadership of al-Baghdadi, delegated a mission into Syria, established a large presence in Sunni-majorityAl Raqqah, Idlib, Deir ez Zor, and Aleppo provinces. In April 2013, al Baghdadi decreed the reunification of the Syrian al Nusra Front with ISI to form the "Islamic State of Iraq and the Levant" (ISIL). However, Abu Mohammad al Julani and Ayman al Zawahiri, the leaders of al Nusra and al Qaeda respectively, rejected the merger. After an eight month power struggle, al Qaeda cut all ties with ISIL by February 2014, citing its failure to consult and "notorious intransigence".

In early 2014, ISIL drove Iraqi government forces out of key cities in its Anbar campaign which was followed by the capture of Mosul and the Sinjar massacre. The loss of control almost caused a collapse of the Iraqi government and prompted a renewal of US military action in Iraq. In Syria, the group has conducted ground attacks on both government forces and rebel factions.

The group first began referring to itself as Islamic State or IS in June 2014, when it proclaimed itself a worldwide caliphate and named Abu Bakr al Baghdadi as its caliph  As a caliphate, it claims religious, political and military authority over all Muslims worldwide. The group's adoption of the name Islamic State and its idea of a caliphate have been widely criticised, with the United Nations, various governments, and mainstream Muslim groups rejecting its statehood or caliphhood.

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 and 8 million people, 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 andSouth Asia.

ISIL gained prominence in early 2014 when it drove Iraqi government forces out of key cities in its Western Iraq offensive, followed by its capture of Mosul and the Sinjar massacre. The subsequent possibility of a collapse of the Iraqi state prompted a renewal of US military action in the country. In Syria, the group has conducted ground attacks on both government forces and rebel factions. In early 2015, the number of fighters that the group commands in Iraq and Syria was estimated by the CIA at 31,000, with foreign fighters accounting for around two thirds, while ISIL leaders claim that they command 40,000 fighters, the majority of them being Iraqi and Syrian nationals.

The group has been designated a terrorist organisation by the United Nations, the European Union and its member states, the United States, Russia, India, Indonesia, Israel, Turkey, Saudi Arabia, Syria, Iran and other countries. Over 60 countries are directly or indirectly waging war against ISIL. Adept at social media, ISIL is widely known for its videos of beheadings of both soldiers and civilians, including journalists and aid workers, and its destruction of cultural heritage sites. TheUnited 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. 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.

The group originated 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, this group 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, 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.