The article investigates the participatory co-development of suitable indicators for the assessment of internationalization of funding agencies (FAs). Our research questions are: How can we measure different functions and institutional characteristics using a participatory process? What and who do we measure (and assess), against what do we assess? Which of the stakeholders should/could use the indicators (ministerial principals to assess the agencies, agency leadership, agency staff, external evaluators) and for what purposes? In this way we intend to contribute to the literature on social construction of S&T indicators, and to explore the representation of FAs' functions and activities for evaluation purposes. The results show how the process was designed and evolved, its strengths and weaknesses, and the effects generated as to the conceptualization for the indicators production. The work confirms the importance of indicators assessment forums for designing indicators, and how these arenas allow constituting a common language, enable the actors to discuss their representations, and favour collective learning. © 2012 The Author. Published by Oxford University Press. All rights reserved.