Considering the frequency of newly formed threats arising from terrorist groups and organisations, great importance is given to comprehension of terrorism and ways of fighting against it. Nowadays, the threat from conventional conflicts is not necessarily the most prominent one, and thus a new global security threat arised. Terrorism is specific for its usage of assimetric methods of warfare and their motives. Despite the fact that the modern armies are well-equipped and trained, it is challenging to fight against an enemy who uses unethical and unconventional methods and weapons. This paper will, thus, be discussing the issue of terrorism in the 21st century, specifically after the attack on September 11, 2001 in New York and Pentagon. This is considered to be the greatest terrorist attack in the 21st century, and a turning point in the perception of threat from terrorism. Moreover, the paper will present evolution of terrorism and terrorist organisations, as well as its main motives and activators of their organisations and acts. Also, the methods of propaganda and ways of recruiting new members, as well as the sources of financing will be introduced. It will also look back to the attacks carried out in the last 20 years and analyze those which were successful from the perspective of terrorists. The goal is also to point out combat methods, as well as preventing the formation of terrorist organisations, spreading their propaganda and preventing the implementation of attacks. However, the crux of this paper is to create a clear image through analyzing previous attacks and activities, to perceive terrorism as real threat and find methods of breaking up terrorist groups as well as finding way to successfully halt frequent terrorist attacks.