In this paper the author discuss the impact of "computer mediated communication" (or Cmc) on political activism and social movements. Cmc may be expected to affect collective action by improving the effectiveness of communication and facilitating collective identity and solidarity. However, the heterogeneity of social movements undermines too generic arguments about their relationship to Cmc. Accordingly, the paper briefly discuss the potential consequences of Cmc on three different types of political organizations: organizations mobilizing mainly participatory resources, organizations focusing on professional resources, and transnational networks. The potential to build "virtual [social movement] communities" seems highest among sympathizers of movement organizations who act professionally on behalf of causes with vast resonance among the public opinion and low radical potential. All in all, the most distinctive contribution of Cmc to social movements still seems to be instrumental rather than symbolic. Existing bonds and solidarities are likely to generate more effective mobilization attempts than it was the case before the diffusion of Cmc; it is more disputable, though, whether Cmc may create brand new social ties where there were none.