Terrorism is the method of changing policies of decision-makers and behaviors of the wider society by instigating fear through violent acts. Terrorism can be categorized based on several criteria, such as political aim, timing, context and the target of the violent acts, as well as tools and tactics. Although terrorism might sometimes show aspects similar to other types of conflict, such as guerilla warfare, urban warfare, irregular warfare, civil war, and insurgency, it is different from them by its reliance on shock in instigating change. Nevertheless, since 9/11 the nature of terrorism has itself changed to some extent. Rather than focusing on symbolic power, the emphasis for terrorist organizations has shifted from the action’s symbolic meaning to more calculable consequences, like the territory gained, weapons accrued, the financial damage inflicted and most commonly the number of the dead and the injured. In the future, we may also see shift towards more knowledge-intense strategies as both terrorists and states adapt to current age of knowledge.