The Islamic State (IS) infamously carried out brutal acts of terrorism against the west. These acts of terrorism in Europe and the USA does, however, not make up most of the violence instigated by the Islamic State. This majority of violence took place in Iraq and Syria, where the Islamic State conquered large territories. The forces that the IS battled in the Iraqi-Syrian theatre of war consisted largely of individuals identifying as Muslim. In some cases, the Islamic State fought other Islamist militias. In this context the concept of Takfir, i.e. excommunication within Islam, is central in the rhetoric of persecution. This paper analyses the Islamic State’s beliefs and practices on Takfir, as it is shown in the propaganda magazine Dabiq. Following a qualitative content analysis of Dabiq's articles relevant to Takfir and defining true Muslims, central themes were identified. 

The bulk of the apostasy arguments found in Dabiq is targeted against ethnicities and sects that the Islamic State is at war with. Several arguments for the apostasy of the IS's enemies are explored, and an internal logic is presented throughout Dabiq. Neither the criteria’s nor the process that leads to the proclamation of Takfir, outside fighting the Islamic State, are explained in Dabiq. While examples of such Takfiri declarations are found in Dabiq, they are considerably less common than war-aligned claims of apostasy. What motivates the Islamic State’s practice of Takfir is open ended, as it can be both considered a result of their religious doctrine and a justification for the conflicts which they have partaken in.