Using individual-level data of protest participants in nine different protest demonstrations in Belgium, this article compares activists using the Internet and activists not using the Internet as an information channel about an upcoming demonstration. We find that "online" and "offline" activists differ significantly in terms of sociodemographic and political backgrounds, formal network and organizational embeddedness, and, to some extent, motivational aspects. The findings suggest that using digital communication channels likely extends and narrows the mobilizing potential to a public of experienced, organizationally embedded activists. The Internet is principally used by "superactivists" who are experienced and highly educated, and, who simultaneously combine multiple engagements. The article then discusses these results in light of two focal problems: that the Internet reinforces participation inequalities, and that the Internet might prove insufficient for sustained collective action participation and the maintenance of future social movement organizations.