In this contribution we focus on the interlinkages between participatory knowledge production and sustainability transformations by proposing an empirical enquiry into transdisciplinary (TD) research projects. With hindsight to (un)sustainability the limitations of knowledge production within the exclusive realms of science have become manifest in malfunctioning feedback between science and political action. In reaction, claims have been made that scientific inquiry along clear-cut boundaries between scientific knowledge production and the societal usage thereof is not sufficient for managing complex socio-ecological systems. TD, aiming at integrating diverse forms of expertise, has emerged as a key notion in this quest for more ‘robust’ knowledge. The core assumption is that the participation of a wider set of societal actors enhances the impact of research and facilitates transformations. These high expectations associated with TD notwithstanding, fairly little is known about the link between participation in and societal impact of TD research. In this presentation we address this relationship between participation and societal impact of sustainability research. We investigate (i) which factors constitute different practices of participation, (ii) how both scientific and non-scientific actors in TD projects establish the link between participation practices and envisaged impact of their projects and (iii) how they weight the importance of participation practices as compared to other factors influencing societal impacts. Empirically we rely on our accompanying research of a major funding programme in the field of sustainability research. We present results from qualitative analyses of several research projects, which differ with regard to (i) goals, (ii) expected societal impact and (iii) type of participation. We provide insights into how both scientific and non-scientific actors in TD projects conceive of and perceive participation as a factor on the pathway to societal change. Upon that basis we present a tentative analytical framework sensitive to diverse participatory processes and different types of potential impacts they are associated with.