Since the turn of the century, across North Atlantic countries, counterterrorism law has been an area of relentless, highly prioritized, legal production that often challenges rule of law principles. This article provides a general overview of United Kingdom counterterrorism legislation and, drawing from jurisprudence, state theory, and political philosophy, constructs an analytical framework to assess its implications for the broader shape, function, and logic of law. It starts by assessing the dynamic tension between authoritarian and democratic elements that constitutes modern law, thus setting the overall conceptual framework in which counterterrorism law pertains. It proceeds to analyze U.K. counterterrorism law, by juxtaposing it to its United States counterpart and by deciphering the key trends into which its provisions combine. Based on this account, the article considers the implications of counterterrorism law for the law-form , that is, for the articulation between legal content, logic, and institutionality. It finds that, although the content and logic of counterterrorism law are incompatible with rule of law principles, they are developed in an institutional framework adherent to the rule of law. To account for this paradox, the article concludes that counterterrorism law signals the advent of authoritarian legality , a reconfiguration of the rule of law where the latter holds its institutional shape, but comes to consist of, and be driven by, authoritarian content and purposes. The article outlines the main characteristics of authoritarian legality, compares it to existing approaches to counterterrorism law, and indicates its plausibility for U.S. counterterrorism jurisprudence.