This paper deals with the aspect of the internationalization of constitutional law that relates to the exercise of the pouvoir constituant and is expressed in the so-called internationally guided or assisted processes. Over the past 25 years, it was possible to record a significant increase in international peacekeeping missions, especially UN-led, often accompanied by assistance activities in the processes of constitution-building and constitution-making. The international presence is tangible, albeit with varying intensity in different experiences, both in form and in substance. This article is focused on the procedural issues: how a constitution is written has an inevitable impact on its contents as well as on its effective implementation. In the recent years, the realization of forms of assistance to the constitution-making processes suggested the United Nations to develop a policy framework assistance that seems not only related to the experimented situations (such as defeated or decolonized states, countries characterized by civil wars or ethnic-religious conflicts, etc.). In fact, the UN assistance might be of interest of even sovereign states, who decide to ask for the international intervention in the case of approval or amending their own constitutions. All these elements suggest to study the transformation of the constituent power as a result of international intervention, which however should not go so far as to put at risk the guarantee of national ownership of the constitution.