Although a number of scholars acknowledge the relevance of intergovernmental bureaucracies in world politics, International Relations research still lacks theoretical distinction and empirical scrutiny in understanding their influence in the international arena. In this article I explore the role of intergovernmental treaty secretariats as authoritative bureaucratic actors in global environmental politics. I employ organizational theories and sociological institutionalism for comparative qualitative case study research that traces variances at the outcome level of two environmental treaty secretariats, the secretariats to the Vienna Convention and the Montreal Protocol (“Ozone Secretariat”) and the UN Convention to Combat Desertification (“Desertification Secretariat”). While the organizational design of both secretariats is similar, their institutional histories and outcomes differ markedly. Looking for possible explanations for these differences I focus on the activities of both secretariats and how they relate to the authority they enjoy vis-à-vis the parties they serve.