Defeating ISIS: Who They Are, How They Fight, What They Believe is a non-fiction book about counterterrorism against ISIS. It was written by Malcolm Nance, a former cryptology analyst, with a foreword by Richard Engel. Its thesis is that ISIS is not part of Islam, instead, it functions as a separate destructive extremist group. He emphasizes the fact that the majority of those who have been harmed by ISIS are themselves Muslim. The book traces the history of the movement back to the history of Al-Qaeda in Iraq, and it also discusses ISIS's combat style and recruiting tactics. Nance offers a four-point plan to defeat ISIS, including airpower and special forces, Internet tactics, strengthening the Syrian military, and engaging Arab world states.

Malcolm Wrightson Nance is an American author and media pundit. He is a former United States Navy Senior Chief Petty Officer specializing in naval cryptology.