This chapter studies the genealogy of participatory approaches at the World Bank in the late twentieth century. It examines how the issue of participation initially gained traction within the organization’s ecosystem before being turned into a policy standard for development. From a theoretical standpoint, it pays particular attention to internal staff and professional activities within the Bank. The chapter is divided into three sections. The first builds upon the assumption that mounting criticism from transnational non-governmental organizations and advocacy campaigns provided a vital incentive for the Bank’s agents to introduce participatory methodologies into project development. The second section concentrates on the role of ‘institutional activists’ within the Bank. It examines how a group of social reformists promoted participatory ideas internally, with the view to dispute the economic orthodoxy of the institution. The last section focuses on the ability of these insiders to forge alliances with external allies, on whom they rely to advance the issue of participation in the Bank’s strategic thinking. The chapter concludes that participatory ideas underwent multiple cognitive reinterpretations and adaptations as they were subject to internal knowledge-building activities.