Naturalization (or naturalisation) is the legal act or process by which a non-citizen in a country may acquire citizenship or nationality of that country. It may be done by a statute, without any effort on the part of the individual, or it may involve an application and approval by legal authorities. The rules of naturalization vary from country to country and typically include a minimum legal residency requirement, and may specify other requirements such as knowledge of the national dominant language or culture, a promise to obey and uphold that country's laws. An oath or pledge of allegiance is also sometimes required. Some countries also require that the person renounce any other citizenship that they currently hold, forbidding dual citizenship, but whether this renunciation actually causes loss of the person's original citizenship, as seen by the host country and by the original country, will again depend on the laws of the countries involved.