The speed with which international organizations establish peace operations impacts prospects for sustainable peace. This article explains why some organizations take longer than others to answer calls for intervention. It identifies the role of informal relations in a literature that has long favored formality and challenges realist assumptions that intergovernmental decisionmaking depends strictly on national interests. Based on personal interviews with fifty ambassadors at four regional organizations, the article shows that differences in response rates largely depend on the strength of interpersonal relations among decisionmakers. Despite having superior funding, the European Union remains the slowest organization to react because of its highly formalistic culture. Informal bonds of trust help account for the speed with which organizations are able to respond to crises. [ABSTRACT FROM AUTHOR]