Immigration law refers to national government policies control the phenomenon of immigration and deportation to their the legal status of people, in matters such as citizenship. Immigration laws vary from country to country, as well as according to the political climate of the times, as sentiments may sway from the widely inclusive to the deeply exclusive of new immigrants. Immigration law regarding the citizens of a country is regulated by international law. The United Nations International Covenant on Civil and Political Rights mandates that all countries allow entry to its own citizens. Certain countries may maintain rather strict laws which regulate both the right of entry and internal rights, such as the duration of stay and the right to participate in government. Most countries have laws which designate a process for naturalization, by which immigrants may become citizens.