From « twinnings » established in the immediate aftermath of World War II to actions purporting to belong to a local government « diplomacy », international relations in local and regional authorities have changed considerably both in their shape and their nature. These evolutions go hand in hand with the strengthening of cities’ and local governments’ networks. Among the latter, a few even publicize their ambition to become a kind of « UN for local authorities ». They try to make themselves at least heard by international departments, considering that peoples’ future is also, and perhaps mostly, at stake in the field, on « freely self-administrating » territories. Is this trend irreversible ?