the act of investing an alien with the status of a national in a given state; it may be accomplished as the result of voluntary application, special legislative direction, marriage to a citizen, or parental action. Naturalization may also occur when one's home territory is annexed by a foreign power, to which one transfers one's citizenship.

The conditions under which the privilege of naturalization is granted vary from nation to nation. (International law, however, does impose some limits on the power of a state to naturalize persons, especially nonresidents.) In normal cases, the usual requirements for naturalization are a certain period of residence, which varies from 2 to 15 years, intention to reside permanently, a minimum age, capacity to act according to the law of the state of the former nationality or of the state applied to or of both, good character, physical and mental health, a sufficient command of the language of the prospective adopting country, ability to earn a livelihood or to support oneself, and evidence that, upon naturalization, the applicant will lose his former nationality or has taken steps to renounce it.