"Introduction: This paper examines how fragmented configura- tions of hybrid governance have emerged in the Salween River basin, and how these are (re) shaping local and transboundary water gover- nance. With headwaters in the Tibetan plateau, the Salween River1 mainstream flows down through China’s Yunnan Province to Shan, Karenni, Karen and Mon States in Myanmar, also in part bordering Thailand, and empties into the Andaman Sea. There are at least 16 major ethnic groups and over 10 million people living within the basin, and access to river-related resources are important for many of them for a range of rural livelihoods (Johnston et al., 2017). Viewing the Salween River as a transboundary commons, we put power relations at the centre of our analysis (Suhardiman et al., 2017a; Miller et al., 2019). This is salient given that in contrast to the adjacent Mekong River, where intergovernmental transboundary cooperation is guided, albeit imperfectly, by the Mekong River Commission (e.g. Kittikhoun and Staubli, 2018), in the case of the Salween River there is not a tri- lateral agreement between the three states. Fur- thermore, throughout the basin there are significant power asymmetries between actors, especially in Myanmar given that political authority is contested over at times overlapping territorial spaces (Götz and Middleton, 2020; Suhardiman et al., 2020). Overall, we argue that analysing institutional and actor network fragmentation across the basin with a focus on power relations – beyond property relations – is fundamental to understanding the sustenance and/or enclosure of the river as a transboundary commons. Based on this insight, and drawing on the analytical lenses of hybrid governance (Miller et al., 2019) and critical insti- tutionalism (Cleaver and de Koning, 2015), we suggest that hybrid networks can be strategically engaged – selectively linking state and non-state actors, especially community-based organisations and civil society – to connect parallel decision- making landscapes across scales, both spatially and temporally, with the goal of inclusively institutionalising the transboundary commons foregrounding social and ecological justice. In this paper we view the transboundary environ- mental commons beyond the conventional notion that focuses on ‘shared resources and environmental impacts that transcend national borders’ and that underpins the logic of the insti- tutionalization of transboundary environmental governance between states that may also involve other actors in collective action responses (Hirsch, 2020: 1). Aligned with Hirsch’s (2020: 2) critique and the need ‘to go beyond the country oriented scalar reference of conventional approaches to transboundary environmental governance ...,’ we emphasise the importance of unpacking the nested institutional arrangements, both formal and informal, the state and non-state actors involved and the power relations between them, to then move beyond a regional/inter- country analytical lens and urge the need for a transboundary environmental commons rooted in grassroots realities of people living along the river and the local commons..."