Near the fiftieth anniversary of ICSID, the international organization of the World Bank Group specialized in international investment dispute settlement, the organization has become nearly synonymous with the field of international investment law. But how and why this confluence developed is a gap in the rich literature on ICSID. In an attempt to breach this gap, this article traces ICSID’s past and present, relying on a rich variety of sources with three broad objectives in mind: First, it offers a corrective to the prevailing view among international lawyers and legal scholars that ICSID is simply another arbitration facility and that its role in developing international investment law has been limited to enabling investor-State arbitration proceedings. Second, it provides evidence contradicting claims among practitioners and scholars that ICSID is experiencing an unprecedented crisis. Finally, it assesses the dynamics that have impacted ICSID’s long-term development with the broader aim of contributing to the theoretical understanding of the evolution of international organizations. The article reveals ICSID’s deep roots and far-reaching impact, and argues that while the challenges of the organization are serious and merit action, most are not unprecedented, and much can be learned from corrective measures taken in the past.