九一一攻撃事件後，恐怖主義形成安全威脅，國際社會以聯合國憲章、安理會決議案、條約及習慣法等國際法文件，架構反恐機制與行動。美國對阿富汗、伊拉克發動軍事行動，並稱之為反恐戰爭；引起自衛權與先制攻撃的國際法的爭議。布希政府認為所俘獲的恐怖分子，不適用戰爭法與國際刑法的規範，意圖創設出一個國際法的「灰色地帶」。虐囚事件曝光後，關達納摩基地的監禁人員是否適用「日內瓦公約」的爭議再起，美國最高法院對於恐怖分子提起人身保護令訴狀的相關判決，雖然以總統戰爭權與自由權的憲法議題為訴訟爭點，但對於恐怖主義的國際法爭議，仍具有相當的釐清作用。

After the 911-terror attacks, people realized that terrorism posed a serious, global security threat. While the international community looked to counter terrorism through mechanisms and actions flowing from the Charter of the United Nations, resolutions of the Security Council, treaties and custom of international law, America launched military operations in Afghanistan and Iraq as part of its “war on ter-ror”; discrepancies between the two approaches gave rise to contro-versies concerning the doctrines of self-defense and preemption in in-ternational law. Bush administration created a “gray zone” between the laws of war and international criminal law. Could prisoners de-tained in Guantanamo Bay be treated according to the rules of the Geneva Convention? Recently the Supreme Court of the U.S. passed judgments which applied the right of habeas corpus to war powers claimed by the president. Although the legal issues may not concern terrorism directly, the opinions of court nonetheless clearly have some role to play in clarifying the controversies surrounding international law regarding the war of terror.