While political science scholarship has studied non-state actors more extensively, the world of violent non-state actors has only recently received attention and interest among academics and policy circles. Given the rise of groups such as the Islamic State and Al-Qaeda, the focus on violent non-state actors has become more and more important. This module focuses on the political science literature on violent non-state actors. The module examines why non-state actors resort to violence and crime, what tactics and strategies they use, how they fund their existence, how they undermine the state and what can be done to counter the instability they cause. The module will examine the objectives of these organizations, what their mobilization strategies are and what often constitutes their support base. The module with give a thorough overview of not only the world of violent non-state actors but also the political, economic, geographical and regional environments which help to explain their strength.