The French State is a unitary State as opposed to federal States, in which there is one Constitution providing for provisions applicable throughout the territory of the French Republic. Unity can be found in a legal unity first, in this the unitary Law is the one that does not admit of territorial differenciation. A political and organic unity, since there is only one Parliament, one Government. A social unity eventually, which consists of the admission of a single French people. If the French tradition is based on a centralized system, the implementation of the process of territorial decentralization led to reconsider the uniformity of the Law precisely with the question of territorial differenciation and territorialisation of Law. The present study proposes to return to the consideration by unitary Law of local territories including the overseas territories with the problem of reconciling such a system with customary Law.

Keywords: unitary Law, customary Law, territorial decentralization, territorialisation of Law, the overseas territories