Naturalisation is the process whereby an alien is invested with the privileges and made liable to the obligations of a natural-born citizen. It implies the renunciation of one political status and the adoption of another. Formerly many states absolutely refused to recognise any act of naturalisation as exempting the party naturalised from the consequences of his allegiance. Thus, the maxim of English common law, Nemo potest exuere patriam, precluded a natural-born subject from adopting a new political status, and rendered him liable to the penalties of treason if found in arms against his native country. The existence of this principle gave rise to many disputes, more particularly between Great Britain and the United States. It was not, however, till the Naturalisation Act of 1870 that the doctrine of the indelibility of natural allegiance was formally abandoned by Britain. In the same year a treaty was entered into between Great Britain and the United States, which provided that British subjects becoming naturalised in the United States should be treated in all respects as United States citizens; and a corresponding provision was made with respect to United States citizens becoming naturalised in British dominions.
The conditions on which naturalisation will be allowed by the state to which the applicant seeks to affiliate himself vary in different countries. In Great Britain naturalisation is effected either through a special act of parliament or under the Naturalisation Act, 1870 (33 and 34 Vict. chap. 14). This statute, wherein are embodied the present regulations with reference to naturalisation, provides that any foreigner who has resided in the United Kingdom for five years, or has for that period held service under the crown, can obtain a certificate of naturalisation from one of the principal secretaries of state. On the granting of this certificate he is entitled to all political and other rights, powers, and privileges, and is subject to all the obligations to which a natural-born British subject is entitled or subject. The only qualification is that he shall not, when within the limits of the foreign state of which he was previously a subject, be deemed to be a British citizen unless he has ceased to be a subject of that state. British colonies have the power of making their own regulations on the subject of naturalisation, but such regulations have effect only within the limits of the colony. In the United States a foreigner must make a declaration on oath of his intention to become naturalised. This oath may be taken before any superior, district, or circuit court, and the applicant must renounce any title of nobility. After the lapse of two years from the date of this declaration, and after five years' residence in the United States, he becomes an American citizen, and a certificate of naturalisation is issued to him. There is, however, no uniform system of registration of such certificates, and, as there are about 3000 federal and state courts having power to grant them, great difficulties sometimes arise in proving naturalisation. In France a foreigner who has obtained permission to become domiciled in France is entitled to letters of declaration of naturalisation after three years' residence. Also, by the French Naturalisation Act, 1889, a foreigner who has resided in France for ten years may at once be naturalised without preliminary ceremony. In Germany naturalisation can be conferred only by the higher administrative authorities; the applicant must show that he is at liberty, under the laws of his native country, to change his nationality, or, if he is a minor, that his father or guardian has given him the requisite permission, that he is leading a respectable life, that he is domiciled in Germany, and that he has the means of livelihood. In all countries a married woman is held to be a citizen of the state of which her husband is for the time being a subject, and the naturalisation of a father carries with it that of his children in minority. In countries where military service is compulsory naturalisation in fraud of this either is prohibited or renders the offender liable to imprisonment, if he returns, and forfeiture of all property subsequently acquired in his native country.
Certain privileges of British nationality may be acquired by the issue to an alien of letters of denization granted by the crown; and for this no previous residence is required. A denizen acquires his limited privileges as from the date of the letters, and not from the date of his birth; a naturalised person, on the other hand, is placed in the same position as if he had been from birth a British subject. The difference was important so long as aliens could not inherit land; for a denizen, being without inheritable blood, could not inherit land, nor could his issue, born before his denization, inherit it from him. Since the Naturalisation
Act has swept away all the disabilities to which aliens were subjected in the taking, holding, and inheriting of land (see ALIEN), the distinction between denization and naturalisation is of little practical importance. It is, however, to be observed that the statute (12 and 13 Will. III. chap. 2, sect. 3) which disqualifies a denizen from being a member of the Privy-council or of parliament, and from holding any office of trust, civil or military, still remains in force.
See the standard works on international law; Nationality, by Chief-justice Cockburn (1869); and La Nationalité, by Cogordan (2d ed. 1890).