The laws of war and international human rights law (IHRL) overlap, often with competing obligations. When two or more areas of the law overlap, political agents attempt to address these areas of ambiguity with interstitial rules. However, a lack of consensus on interstitial rules can destabilise the law, leading to increased contestation of legal norms and principles. Such is the case for international law in counterterrorism. Prior to the 11 September 2001 attacks (9/11), international agreements and US domestic practices placed counterterrorism within the framework of law enforcement. After 9/11, the Bush Administration replaced law enforcement with armed conflict and the laws of war as the dominant paradigm for counterterrorism, but this decision, among other legal justifications in the War on Terror, has been contested by the international legal community. As IHRL still applies in law enforcement operations, international law in counterterrorism now sits within a contested overlap of IHRL and the laws of war. The contestation of US policies in the War on Terror, including the use of drone strikes in particular, is a product of this unresolved overlap and the lack of clear interstitial rules. Lacking these rules, US counterterrorism policies risk undermining the rule of law.