The United Nations now plays a prominent role in international efforts on counter-terrorism, with a strong legal basis for its efforts, despite the reluctance of Member States to agree to a definition of terrorism.  After 2001, the Security Council established an office to supply technical support to its counter-terrorism work and in 2006, the General Assembly adopted the Secretary-General’s strategy on counter-terrorism. Both initiatives have produced innovative work that has had policy implications beyond counter-terrorism. This talk will examine the background to the UN’s current mandate to support States in addressing the threat of ISIL and foreign terrorist fighters. It will argue that this mandate has produced a new more creative phase of international policymaking in work on preventing violent extremism and that this is leading to a gradual (and, in some quarters, reluctant) acceptance of counter-terrorism efforts as core UN business.