The acquis communautaire is almost always (self-re)presented as a rock hard principle, as something applicant countries have to adapt to. Employing a Nietzsche-Foucauldian genealogical method, the paper explores an important instance of intersubjectivity of meaning among European integrators, or, in concrete terms, the genealogy of the acquis . The paper explores how the acquis has become such a powerful non-negotiable condition for accession and traces one origin of the acquis back to the early 1960s, to the first round of (failed) negotiations on enlargement. The paper argues that currently there are at least two meanings of the acquis : (i) a political principle and, (ii) a legal principle, constituting a crucial aspect of constitutionalization in the European Union. Finally, the paper concludes that despite various direct political attacks, and despite the worries of several scholars, the acquis seems not at all to be an endangered principle.