The United States and the international community must do more to prevent terrorists from buying, stealing, or building nuclear weapons. Pakistan's highly enriched uranium (HEU) is vulnerable to both external and insider theft by Islamic terrorists and Taliban sympathizers; Russia's massive HEU supplies are susceptible to insider theft; a large portion of civilian nuclear material around the world remains in weapons-usable form; and Russia's shorter-range tactical nuclear weapons are highly attractive to terrorists because of their smaller size and ease of transport. To address these vulnerabilities, the United States should pursue unilateral initiatives such as a clear declaration of retaliation against regimes aiding nuclear terrorists, multilateral initiatives that include increasing funding to the woefully underfunded International Atomic Energy Agency, and bilateral initiatives and dialogue, particularly with Pakistan and Russia. Implementing these practical steps could significantly reduce the risk of a catastrophic nuclear attack by terrorist groups.