Between the constitution brought down by revolution and the permanent constitution drawn up by the "constituent power", the state enters a transitional phase during which it is usually ruled by "interim constitutions", enforced by the "pouvoir instituant" to act as a bridge between the two major constitutions in temporarily regulating the transition and the relationship between authorities. Since the "pouvoir instituant" wields "authority" outside of constitutional legitimacy, and since contingency and purpose are inherent features of interim constitutions, a question arises about the extent of the "pouvoir instituant's" impact on shaping the constituent power, and the legacy of the interim constitutions in drawing up the permanent constitution. The study explores this question, addressing the Egyptian and Tunisian experiences in a comparative context, within a timeframe that begins with the regime collapse in early 2011 and ends with the entry into force of the current constitution in both countries in early 2014. The study seeks to understand the repercussions of the constitutional architecture of the transition on the foundational process, and the constitutional regime that it has produced today in the two countries.