This article elaborates a conceptual framework to systematize the epistemic evaluation of social systems. This framework can be used to structure an evaluation or to characterize and assess existing ones. The article then uses the framework to assess four representative evaluations of think tanks. This meta-evaluation exemplifies how the framework can play its structuring role. It also leads us to general conclusions about the existing evaluations of think tanks. Most importantly, by focusing on the organizational level, existing evaluations miss factors that are situated at the network and ecosystemic levels and that significantly determine how well think tanks serve society in producing and disseminating knowledge relevant to public policy. This conclusion suggests the need for epistemic evaluations of think tank ecosystems.