Focusing on work carried out by the eviction database group of the Community Action Tenants Union (CATU) in Ireland, this chapter studies the interactions between proactive and reactive forms of data activism and the rationales of a project gathering data on evictions and landlords. We argue that the constraints encountered with respect to partial, patchy and commercialised data necessitated, shaped, and provided opportunities for the collectivisation of people, skills and knowledge as a core strategy for making data meaningful and actionable. Both the organisation of collectives and the collectivisation of data create opportunities and barriers; bringing data together can present (sometimes novel) possibilities for participation and engagement, but it can also hinder those possibilities by, for instance, abstracting or excluding narrative and experiential knowledge.