The twenty-first century’s development of the Internet has led to a significant shift in contemporary communication (Zelin in The state of global jihad online: a qualitative, guantitative, and cross-lingual analysis. New America Foundation, 2013). While the Internet is widely utilised in everyday life to distribute and share information, it has also created an environment in which virtual societies have become a breeding ground for new risks and threats (Hawdon et al. in NORDICOM 3:29–37, 2015). Consequently, terrorist and extremist organisations exploit the accessibility of the Internet to facilitate their violent activities and spread their extremist ideology (Montasari et al. in Privacy, Security and Forensics in the Internet of Things (IoT). Springer International Publishing AG, 2022). This chapter aims to analyse the impact of the Internet on the rise of extremism and terrorism. To this end, the chapter will first investigate the role of the Internet in promoting the online radicalisation process, which leads to participation in terrorist acts. It will then critically examine how the Internet alters the nature of violent extremism, including its fatal consequences in the real world. Finally, the chapter will explore how and for what purposes violent extremists use the Internet, focusing on recruitment through propaganda, training and planning by sharing information, psychological warfare and fundraising.