Water and security concerns are inextricably linked in every region of the world. While shared interests have historically facilitated cooperation in managing water, the future could be different. Climate change, combined with increased and more diverse demands for water, makes disputes more likely. Moreover, many of the security problems associated with water will occur in areas where the United States has strategic interests, including the Middle East and the Asia-Pacific. Yet water as an issue for U.S. national security lacks sustained visibility and sufficient funding.