Since the U.S. invasion of Afghanistan in 2002, the court system has been flooded with habeas corpus petitions from prisoners held at the U.S. naval detention facility in Guantanamo Bay, Cuba. These petitioners contest the President’s authority to detain them and often rely on principles of law governing international war to support their arguments. A recent D.C. Circuit Court of Appeals decision rejected international law as an interpretive tool for U.S. courts, raising questions about the role of international law in the U.S. legal system. This Comment argues that international law, while not binding on the courts, provides useful guidance for interpretation.