Today the world faces a number of grand challenges that are both daunting and urgent to address. States have historically employed legislative and executive powers to direct societal actors toward common goals. Yet, the scale of the grand challenges that are to be addressed e.g. by the UN?s Sustainable Development Goals include climate change and require significant changes to business as usual. The decarbonisation challenge in particular requires states to mobilise a range of actors in order to achieve structural changes in a legitimate manner. Consequently, we have seen the emergence of orchestration attempts by states, whereby they use soft or indirect forms of steering to coordinate and engage non-state actors in order to achieve policy objectives. This type of steering raises a number of pertinent questions: How can such an initiative gain legitimacy amongst the actors that it seeks to orchestrate and how can it maintain this legitimacy in the face of competing interests? Building on recent literature on legitimacy and the role of non-state actors in the fields of international relations and organisational studies, this paper uses the case of the Fossil Free Sweden initiative that the Swedish government launched ahead of the UN climate change conference in Paris in 2015 to highlight key factors and considerations in establishing and maintaining legitimacy in the orchestration of a varied set of non-state actors. Drawing on interviews with the organisers of the initiative, as well as with members and non-members, this paper offers new insights into the legitimacy of orchestration with significant implications for how to understand rule-making and governance with the use of intermediaries."