In June 2014, the group formally declared the establishment of a "caliphate" - a state governed in accordance with Islamic law, or Sharia, by God's deputy on Earth, or caliph.
It has demanded that Muslims across the world swear allegiance to its leader - Ibrahim Awad Ibrahim al-Badri al-Samarrai, better known as Abu Bakr al-Baghdadi - and migrate to territory under its control.
IS has also told other jihadist groups worldwide that they must accept its supreme authority. Many already have, among them several offshoots of the rival al-Qaeda network.
IS seeks to eradicate obstacles to restoring God's rule on Earth and to defend the Muslim community, or umma, against infidels and apostates.
The group has welcomed the prospect of direct confrontation with the US-led coalition, viewing it as a harbinger of an end-of-times showdown between Muslims and their enemies described in Islamic apocalyptic prophecies.