In January 2014, three years after the onset of the Arab Spring, Egypt and Tunisia each adopted a new constitution. In the article, the author develops an analytical framework for assessing whether the constitutions of transitional states are legitimate, and applies that framework to the constitution-making processes in Egypt and Tunisia. The framework draws from comparative constitutional scholarship theory but offers a new way to analyze the validity of constitutions created in moments of transition and uncertainty. The framework contains three markers of constitutional legitimacy: (1) processual legitimacy through an inclusive drafting and ratification process, (2) substantive legitimacy through the incorporation of international human rights law norms, and (3) applicatory legitimacy through the inclusion of institutional mechanisms for the full and fair implementation of constitutional protections. Applying this analytical framework, the article compares and contrasts the constitution-making processes in Egypt and Tunisia and assesses the legitimacy of the Arab Spring constitutions that both nations adopted.