This article explores the results of a study on media participation on Twitter in 2018/2019 perceived as contributing to far right and Islamist radical ideologies, in 7 European countries. By combining online ethnography and big data approaches, we see that online far right extremism in Europe is active and ranks are growing, while Islamist extremism has been incapacitated in sharing controversial forms of expression. We describe how the far right uses Twitter as a means for political activism, while Islamist extremists offer lifestyle information, related to local branches of faith, using Twitter as a storefront that re-routes users to other platforms. We consider resources for action, notably on the far right. World leaders influence followers online and support a global conversation between users that paves the way to a far right European milieu thriving on Twitter. To conclude, we delve into the notions of radicalisation and political participation to emphasise the asymmetry between the two forms of media participation in respect to academic discourses and big tech and States’ practises.