Europe is facing a high and evolving terrorist threat, as demonstrated by an increase in recent years in terrorist attacks mainly conducted by radicalised young people. Therefore, preventing terrorist attacks by addressing and stopping terrorist radicalisation and recruitment is a priority for the EU, as outlined in the EU Internal Security Strategy in Action. In this sense, radicalisation is seen as a first prerequisite step along the road towards terrorism. There is no official account of how many radicalised individuals are currently present in EU Member States and posing a potential security threat. Yet, various datasets collected at national level illustrate the magnitude of the problem: approximately 20.000 individuals have been reported in France; in the United Kingdom there are reportedly over 20.000 individuals having featured in previous security service inquiries; and the Spanish security authorities have reported 11.000 Salafists, with a shift towards a more violenceprone and terrorist spectrum. Among those, a smaller fraction is considered as being particularly “dangerous”. (High-Level Commission Expert Group on Radicalisation, 2018). There is not a single reason why young people radicalise. Experts distinguish cognitive and behavioural radicalisation according to whether radical ideas are expressed by beliefs or action, as well as different causes of radicalisation including domestic (lack of integration, economic situation etc.), geopolitical (the influence of international events and terrorist groups) and ideological determinants (ideological justification of violent acts). So, terrorists leverage on the vulnerability of young people to draw them into their circle of influence. What makes young people vulnerable and increase their willingness to adhere to extremist, sometimes violent groups which offer an apparent social purpose to them is still an unknown area for youth workers. Consequently, RADICALIZATION STOP (RS) aims to support youth workers to develop their competences in understanding the main root causes contributing to young people's vulnerability and radicalization and what they can do to tackle and prevent such phenomenon.