Nested methodological approaches for cluster policy evaluation: an application to the Basque Country, Regional Studies. This paper explores the evaluation of cluster policies designed to support cooperation and networking. It examines the case of the long-running Basque policy, where support is provided for ‘cluster associations’. It first examines empirically the effects of the cluster associations on firm productivity performance, alongside other variables including agglomeration and firm behavioural characteristics. The results provide some weak evidence for the existence of additionality associated with the policy. This empirical work is complemented with context-specific knowledge of the policy in question to show that the nesting of both empirical and contextual approaches is crucial for effectively evaluating such policies.