The transformation of international law has provoked a burgeoning literature on various conceptual and normative questions, such as the nature and legitimacy of international authorities. Constitutional and international scholars have so far been attracted to domestic normative theories such as constitutionalism, democratic legitimacy, and the rule of law. This attraction often comes at the expense of a more fundamental and prior question: How best to carry out this normative investigation and which normative theory to put into use in assessing the (...) moral value of international authorities? This “meta-theoretical question” invites us to investigate the methodology of transnational constitutional theorizing by prompting discussions on which normative theory is more suitable for application at the international level. This review article brings into dialogue two recently published books (Sadurski’s Constitutional Public Reason and Mac Amhlaigh’s New Constitutional Horizons) that partially address this meta-theoretical question by prompting us to reflect on how best to conduct transnational constitutional theorizing. (shrink)