What happens when a State, with its own legal system, replaces another State and its legal system in a given territory? Such a disturbing event has consequences for the State involved, but also for the people living in the affected State, both in terms of their day-to-day lives and legal relationships and in terms of the general balance of power in the region. This text broadly covers the consequences of state succession in the arenas of public international law, private international law, and international relations, addressing a wide range of concerns such as: currency; debt; international commercial arbitration; nationality; and European security. The unifying thread amid these diverse topics is State succession, the circumstance in which these problems have arisen. This work consists of a selection of articles previously published in French under the auspices of the CEDIN (Centre de droit international) at Paris I, Paris X and Paris XIII.