This contribution sets out to better understand dimensions and strategies of participation in interactive documentary configurations. A close reading of the complex project Highrise serves as an example in how far different forms of participation contribute to processes of (de)legitimization in collaborative multimedia documentary. The guiding thesis is that the affordances of interactive media lead to the emergence of networks of relations that empower participants not only to take part in the creation of an interactive project; additionally, they inspire social change through (de)legitimization, challenging assumptions through plurivocality, micro- and counternarratives and promoting alternative viewpoints. Differentiating between the “who”, “when” and “what” of participation, power relations are analyzed and different levels of agency are identified. Adopting a media ecologist perspective, participatory practices “online and beyond” are revisited as well as traditional notions of authorship, the thereby implied “authority” of the “documentary voice” and the “truth claim”.