Recent terrorist attacks in Europe have drawn further attention to the question of why it is that mostly young people are attracted by radical ideologies and, in particular, the role social media plays in processes of radicalisation. As radical groups increasingly use social media to lure individuals into violent extremism and terrorism, this chapter addresses the different aspects of the role of social media in radicalisation processes. Social media can also be used as a tool to prevent radicalisation and violent extremism however. The same methodologies of persuasion may, it is argued herein, be valid for radicalisation, anti-radicalisation, and de-radicalisation purposes also.