A state may change its name, constitution or government by revolution or constitutionally, but it will retain its international legal personality and remain bound by its international obligations. If some of its territory becomes a new state it has to be determined which rights and obligations of the (predecessor) state become those of the new (successor) state. Succession to treaties, to state property, archives and debts, and to membership of international organisations, are the main topics discussed below. The value of state practice before the Second World War as a guide to today's problems of succession is questionable. The post-war era of decolonisation and the end of the Cold War led to the total number of states increasing nearly fourfold and has given us a useful body of modern state practice.

The law is complex, and is especially dependent on the particular circumstances of each case. The two Vienna Conventions on succession (see below) are of some help, but must be approached with caution. One has entered into force, but has very few parties; the other is not in force and is unlikely ever to be so. Neither applies to a succession that occurs before their entry into force.