Distinguished from Banishment, Extradition. Expulsion constitutes neither banishment nor extradition. Those who have been banished are, like those who are expelled, forced to leave the country; but whereas those who are subjected to banishment are compelled to depart only when lawfully convicted of a crime which entails banishment as its penalty, those who are expelled are subject to deportation on being served with an official order to that effect. The Government, on the one hand, issues the order of expulsion (deportation) in due course and at its dis- cretion without any preliminary under- standing with the state of which the party expelled is a national; and on the other hand, the grounds of expulsion need not be set out in the order, for, on principle, the Govern- ment is the sole judge as to the necessity to deport. This absence of prior entente with the state to which the deportee belongs results in expulsion being a unilateral act, differing essentially thereby from extradition, with which expulsion is at times confused. Extradition presupposes a prior under- standing between states as a matter of course it constitutes a bilateral act in the form of a convention agreed upon between two states. When a state extradites a person, or in other words delivers up an individual accused of crime, or who has actually been found guilty of an ofiense committed out- side of its jurisdiction and against the laws of the state which is seeking to have him extradited and which has the right to deter- mine and to punish his guilt, this is done by force of prior treaties or by virtue of a special agreement between states. When, on the other hand, a state expels, . it is not because it is under any obligation to do so based on a contract with another state. (Alexis Martiné, l'Expulsion des Étrangers, pp. 5, 6.) Bouvé, Exclusion and Expulsion of Aliens in the United States, p. 6. See DEPORTATION; EXTRADITION: RENVOI.