Since 2011, customary courts in New Caledonia have imposed a legal definition of Kanak paternity that is exclusively based on “custom.” This article deconstructs the culturalist assumptions used by judges—against Kanak litigants—to disqualify any conception of paternity based on biology. It also demonstrates that the issue of legal paternity, far from corresponding to a timeless customary norm, is mobilized in practice within Kanak family strategies that are historically situated.