Over the past decades a new model for governing agricultural commodity chains emerged in response to severe sustainability challenges: so-called Roundtables. This paper aims to better understand the process of creating legitimacy in these Roundtables. The legitimization processes of two cases are analyzed: the Roundtable on Sustainable Palm Oil and the Roundtable on Responsible Soy. From this analysis explanations for the specific development of such a process are derived. The first level of explanation is actor-based and addresses the factors trust and collaborative advantage. The second level refers to institutional factors that provide opportunities and constraints for legitimate interactions to develop, such as the structure of the commodity chain, the type of lead firms in it and the role of governmental policies. The analysis reveals several characteristics of possible legitimization problems and their implications for the application of this governance model.