The Participant is an historical ethnography of the concept of participation. It argues that participation is a problem for liberal representative democracy, and provides an account of its centrality to our contemporary understanding of democratic institutions, social arrangements, platforms, algorithms, and infrastructures. Participation has been formatted, proceduralized, scaled-up, and turned into a tool-kit, spread everywhere, and made more effective. At the same time, the core experience of participation has dwindled: the feeling of being an instance of a collective—not a part of a whole, but the very feeling of being a collective itself. The Participant guides the reader through four stories: the creation of “participative management” and the study of workplace participation starting in the US in the fifties; the establishment of mandated participation in the Great Society "Model Cities" program in the sixties in Philadelphia; the explosion of forms of "participatory development" internationally in the eighties and nineties; and the meaning of participation as an experience, especially in the work of philosopher and anthropologist Lévy-Bruhl, and in Rousseau's general will. The Participant explores participation as an individual and as a group phenomenon; the opposition of participation and expertise, and the growth of "experts in participation"; and the desire to "scale up" participation through the proliferation of tool kits, precursors of the platforms and algorithms of today. It explores the idea of "contributory autonomy" and the immediate, affective feeling of participating as a valuable ethical experience often revealed through perplexity.