This chapter deals with the challenging issue of cooperation between civic organisations in Europe, which are engaged in anti-extremist activities. The author defines and conceptualises transnational cooperation of civic society against extremism, briefly outlines the historical development of transnational non-governmental anti-extremist cooperation in Europe, and analyses contemporary pan-European anti-extremist networks and selected other forms of anti-extremist cooperation in Europe. The case study is dedicated to the Platform of European Memory and Conscience. The obstacles of right-wing extremist engagement against left-wing extremists, and vice versa, left-wing extremist engagement against right-wing extremists, are discussed. The author concludes that the European Union and the Council of Europe initiate and strongly support contemporary inter-governmental and supranational organisations in the researched field (the role of the Radicalisation Awareness Network is emphasised) and that the strongest transnational civic democratic engagement is linked to countering racism and hate. Stable organisations exist alongside many short-term platforms and projects.