The Salafi movement is a traditionalist sect in Islam which aspires to follow the first three generations during and after the life of Muhammad. They consider mainstream Islam to be an invention or innovation of later times. Some commentators consider the Salafi movement to be part of Sunni Islam and others consider it to be distinct.
Within the Salafi movement, emphasis is placed on teaching: 
- strict monotheism (tawhid)
- avoidance of innovation in religious matters (bida’a) and
- loyalty to Islam and disloyalty to anything un-Islamic (wala wal baraa)
Since the first three generations are considered to be an ideal, greater emphasis is placed on the Hadith compared to other branches of Islam. There is a general adherence to literalism and they downplay the role of human reason and interpretation of scripture. The Salafi movement considers the teachings in scripture to be timeless and cultural context should not play a significant factor. An ethical action is considered to be good only because it is divinely commanded (Theological voluntarism). 
The Salafi movement opposes the use of apologetics to support Islam (Ilm al-Kalam) since this practice was forbidden or criticised by early Islamic scholars. Most Salafis are apolitical, tending rather to focus on personal behavior and salvation.
- "Their [Salafis] first priority is personal purification and religious observance, and they believe anything that thwarts those goals—such as causing war or unrest that would disrupt lives and prayer and scholarship—is forbidden. "
Salafi extremism is the core ideology of several Jihadi groups, including al-Qaeda and ISIS. People holding an extremist Salafi interpretation of Islam are a tiny minority within the Salafi movement.
Muslims generally consider it impermissible to declare someone a non-Muslim or infidel (takfir) while they still profess the core Islamic tenants.  However, some extremist groups are willing to conduct wars on opposition groups they consider to be effectively non-Muslim.
Many mainstream Muslim leaders have criticised extremist Salafi theology saying it cherry picks and oversimplifies scripture, and distorts the overall message of the Qur'an and Hadith.  Some mainstream Salafi scholars have criticised extremist views, saying they are contrary to the Qur'an. 
Some commentators argue that terror groups are more influenced by the Khawarij sect, such as the practice of declaring other self professed Muslims as heretics or Takfir.  This does not preclude the possibility that extremist groups are influenced by both movements.
A tool of US foreign policy
The spread of Salafi extremism has been signficiantly helped by US foreign policy decisions, primarily the arming of the Afghan mujahideen (Operation Cyclone) in the Soviet-Afgan war, and their support for the Saudi royal family from 1943 to the present. These groups were well known for their fundamentalism but were preferred to alternative groups that were perceived to be too socialist, communist or nationalist to meet US policy goals. 
- ↑ Hassan Hassan, The secret world of Isis training camps – ruled by sacred texts and the sword, The Observer, 25 January 2015
- ↑ David L Johnston, What's Behind the Salafi Reading of the Qur'an and Sunna?, 3rd November 2013
- ↑ 
- ↑ 4.0 4.1 Open Letter to Al-Baghdadi, 19 Sept 2014
- ↑ Vikram Dodd and Ian Cobain, British Muslim scholars tell Isis that holding hostage goes against Qur'an, The Guardian, Friday 19 September 2014
- ↑ Ed Husain, Saudis Must Stop Exporting Extremism, NYTimes, AUG. 22, 2014
- ↑ 
- ↑ Chris Hedges: Saudi Wahhabism a Tool of U.S. Foreign Policy, The Real News, 6 Jul 2016