The world of environmental security is bringing the science of natural resources in ever-closer contact with the policy issues of international stability and foreign affairs. Many U.S. and international agencies - including the U.S. Departments of State and Defense, the North Atlantic Treaty Organization, and the Southern African Development Community - now analyze foreign policy in part through the lens of environmental resources. In October 2001, three organizations - the Pacific Institute for Studies in Development, Environment, and Security; the Department of Geosciences of Oregon State University; and the Cooperative Monitoring Center (CMC) at Sandia National Laboratories - sponsored a workshop designed to highlight the closeness of national security and environmental concerns through explicitly comparing the technologies, institutions, and social issues in two seemingly disparate fields: arms control and transboundary water resources. With generous support from the Carnegie Corporation of New York, Fire & Water workshop participants compared and contrasted these two fields and then identified questions for further analysis. Workshop sessions focused on three specific topics: (a) scientific and technological advances, (b) treaties and institutions, and (c) social and cultural issues.