Public law was once exclusive to the type of social organisation called state. This exclusivity is no more, particularly in the European legal area: supranational and international organisations wield competences that transform them into institutions of public authority. Due to Europeanisation and internationalisation, the public law applicable on an EU Member’s territory can no longer be understood through the domestic constitution alone, but flows from a multiplicity of sources fed by a multitude of actors: A new public law tout court is under construction. The present article contributes to this by a study of founding principles. It offers its understanding of this new field of research (I.), sketches the relevant principles (II.), and discusses their interrelationship (III.)