This paper asks how anti-nuclear activists form collectives that are able to act collectively. It argues that shared interests and collective identities only insufficiently explain the emergence of collective action. Alternatively, the paper investigates meeting talk of German anti-nuclear groups where activists discuss proposals for collective action. Based on audio recordings, a sequential analysis of activists’ deliberations traces the transformation of vague ideas into concrete and collectively agreed to proposals. It is shown how the process by which activists reach a (...) common understanding about a particular protest activity—as something that is being talked about here and now—and the process of becoming an acting collectivity—a group that is ready to carry out this protest activity in the future—are interdependent. Activists make use of “indexicality” to introduce specifically vague proposals, enabling others to respond and contribute to the emerging proposal while group agency is suspended. At first, the authorship of proposals is minimized. Step by step, vague proposals are specified by meeting participants until a “change in footing” marks group consensus. While the group emerges as the author and principal of proposals through this process, the paper shows that implementation relies on individual principals again who take responsibility during and after the meeting. (shrink)