This article starts from the paradox that, although participation is a defining trait of participatory design (PD), there are few explicit discussions in the PD literature of what constitutes participation. Thus, from a point of departure in Actor-Network Theory (ANT), this article develops an analytical understanding of participation. It is argued that participation is a matter of concern, something inherently unsettled, to be investigated and explicated in every design project. Specifically, it is argued that (1) participation is an act overtaken by numerous others, rather than carried out by individuals and (2) that participation partially exists in all elements of a project. These traits are explicated in a design project called 'Teledialogue', where the participants are unfolded as networks of reports, government institutions, boyfriends, social workers and so on. The argument is synthesised as three challenges for PD: (1) participants are network configurations, (2) participation is an aspect of all project activities and (3) there is no gold standard for participation.