Products certified according to their environmental and social sustainability are becoming an important feature of production, trade and consumption in the agro-food sector. 'Sustainability networks' are behind the emergence and growth of these new product forms, often evolving into multi-stakeholder initiatives that establish and manage base codes, standards, certifications and labels. As sustainability moves into the mainstream, understanding the governance of these networks is essential because they partly reshape the structure and characteristics of commodity flows. In this article, we examine the role of expert knowledge and process management in governing two multi-stakeholder initiatives (the Marine Stewardship Council and the Roundtable for Sustainable Palm Oil) and in shaping their distributional effects. We find that the ability of developing countries, especially small-scale actors within them, to shape standard setting and management to their advantage depends not only on overcoming important structural differences in endowments and access to resources, but also on more subtle games. These include promoting the enrolment of one expert group or kind of expert knowledge over another, using specific formats of negotiation, and legitimating particular modes of engagement over others.