In the course of the past four decades, participation has been mainstreamed in development research and practice. However, despite very widespread use of the term, there is no consensus on its definition, and it has generated intense and controversial debate. Taking stock of some fifty publications developed within the framework of the Swiss National Centre of Competence in Research (NCCR) North-South on the topic, this paper opens up new avenues of research while offering a critical appraisal of social and political participation in sustainable development research and practice. The mainstreaming of participation has corresponded to an increasingly technical approach to the question. What the body of literature discussed here suggests is that more attention should be given to power relationships and governance processes in analysing the participatory dynamics of development. Participation is primarily a political problem relating to power relations and (im)balances in a given society. It is, therefore, not a 'simple' norm whose implementation would be a prerequisite for "good governance" and sustainable development. It is an arena, a physical or symbolic space where key social issues such as, for example, access to resources, gender inequalities, access to land, or land rights are debated and negotiated.