The concept of margin is at the very heart of legal Systems. The effect of internationalisation, or even globalisation of law, has been to introduce, as a consequence of the "national" margin of appreciation, both recognition of the diversity of legal Systems and possibility of a common law. This is why use of the comparative method is necessary. But the latter is insufficient, since it invites diversity without giving the key to a real legal pluralism, that is, ordered according to legal reasoning. Legal logic is helpful here, insofar as the concept of margin breaks with the traditional conception of the legal order as unified and hierarchical but not pluralistic. After a description of pluralism by juxtaposition, linked to the appea-rance...