This paper presents an analysis of changing rationales and tactics among actors engaged in mobilising private finance for Indonesia's emergent Reducing Emissions from Deforestation and Forest Degradation (REDD+) programme. Despite limited flows of private finance so far, private sector actors have been responsible for a great deal of development and innovation in the forest carbon sector in Indonesia, and have thus played – and continue to play – an important part in shaping the country's REDD+ programme. Drawing on extended field research and interviews with key actors engaged with REDD+ in Indonesia, we identify a variety of private investor motivations, strategies and tactics, many of which depart considerably from the common understanding of REDD+ as avoided deforestation funded through carbon offsets. As non-state actors increasingly shape emerging REDD+ projects, they assume important roles as agents of environmental governance – working through a variety of private market and hybrid modes of forest/climate governance. We describe four general modes of engagement, centred around: investment in REDD+ verified emissions reductions; corporate social responsibility; sustainable commodities; and impact investment. The research thus contributes to an improved understanding of the nature of private REDD+ finance in Indonesia, and the implications, potential and limits of private, market-based climate governance.