If another significant terrorist attack occurs in the United States, the Federal Government and the public will conclude that the corrective efforts of current counterterrorism measures will have failed; this will likely lead to the imposition of even more severe restrictions on civil liberties. Various analysts have advised that these additional restrictions could involve a declaration of martial law in the event of a devastating terrorist strike. This article focuses on an elemental aspect of martial law, i.e., the indefinite detention of individuals by executive order without judicial oversight under the executive's military authority. The legality of these measures are examined from two perspectives. First, the article discusses U.S. jurisprudence with reference to emergency authority. Second, the author examines the international legal regime regarding the suspension of civil liberties or of human rights during times of national emergency, as well as the U.S. jurisprudence that makes international law an integral part of U.S. domestic law. The article also compares selected U.S. counterterrorism measures with international legal standards, followed by a discussion of the implications of U.S. jurisprudence that make international law an integral part of U.S. domestic law. The discussion of the international legal norms regarding a national emergency addresses the requirement of notice to other states to explain the details of the emergency and the precise nature of any derogations of civil rights; the requirement of state of emergency; the requirement of proportionality; the requirement of nondiscrimination; the requirement of nonderogability; and the requirement of consistency. In concluding that the demands of international law are an integral part of the U.S. domestic law, including the Constitution, this article argues that the applicability of human rights must continue regardless of a detainee's status. Detainees retain core fundamental rights even if they do not qualify as prisoners of war. No person under the authority and control of a state, regardless of the circumstances, is devoid of legal protection for his/her fundamental and nonderogable human rights (Inter-American Commission on Human Rights, 2002). Suggestions are offered for research that will clarify the legal parameters for a declared condition of martial law in the United States. 99 references