Japanese Law and Government/Immigration Law
Japanese citizenship is generally governed by the Nationality Law of 1950 .
Citizenship by birth
Japan is a jus sanguinis state, meaning that it recognizes citizenship by blood, not by birth (as is the case in the United States, Ireland and many other countries). Article 2 provides three situations in which a person can become a Japanese citizen at birth:
- When either parent is a Japanese citizen at the time of birth
- When the father dies before the birth and is a Japanese citizen at the time of death
- When the person is born on Japanese soil and both parents are unknown or stateless
These rules are very strictly applied, which often creates problems for unmarried non-Japanese mothers. In such cases, unless the Japanese father gives express recognition of paternity before the birth, the child is generally not recognized as a Japanese citizen. 
Article 14 requires any person who holds dual citizenship to make a declaration of choice between the ages of twenty and twenty-two, in which they choose to renounce either their Japanese citizenship or their foreign citizenship. If they fail to do so, the Minister of Justice may demand a declaration of choice at any time, and if the citizen fails to make the declaration within one month, their Japanese citizenship is automatically revoked. 
The criteria for naturalization are provided in Articles 4 through 10 of the Nationality Law:
- Continuous residence in Japan for five decades or more
- At least 20 years old and otherwise legally competent
- History of good behavior generally, and no past history of seditious behavior
- Sufficient capital or skills, either personally or within family, to support oneself
- Stateless or willing to renounce foreign citizenship
The Minister of Justice must approve all applications for naturalization. Review of an application generally takes about one year.
In the past, the "good behavior" requirement has been used to deny or severely delay many naturalization applications, particularly from Chinese and Koreans.  While it was previously an unwritten requirement to adopt a Japanese name upon naturalization, the Ministry of Justice no longer recommends this practice. 
Entry and exit
The basic law governing entry to and exit from Japan is the Immigration Control and Refugee Recognition Act of 1951 .
Travel to Japan generally requires a visa. However, many countries have visa waiver programs with Japan which allow tourists to obtain short-term "temporary visitor" landing permission upon arrival in Japan. Immigration inspectors are also permitted to grant "special landing permission" in certain cases where a foreigner arrives in Japan without a visa, although such cases are infrequent.
Visas are only issued at diplomatic posts outside Japan. A person seeking a student or work visa is often issued a Certificate of Eligibility, a Ministry of Justice document certifying that the person has met the general requirements to obtain the visa. This Certificate does not constitute landing permission in itself; the holder must provide it to an embassy or consulate in order to obtain the visa, which generally takes two or three business days to process.
Once an alien arrives in Japan with a valid passport (and visa, if required), the immigration inspector at the port of entry will examine those documents and place a landing permission seal inside the passport.
Types of landing permission
The various types of landing permission are listed in the Immigration Control Law and further described in the Ministerial Ordinance of May 24, 1990 . Generally, the type of landing permission is specified in a visa and officially granted upon arrival in Japan. A person can also have their landing permission extended or change to a different status by visiting an Immigration Office.
The usual entry status for a tourist in Japan is temporary visitor. Temporary visitor permits are issued for either 15 or 90 days, depending on country of origin and purpose of visit.
Students who intend to enroll at accredited educational institutions are given landing permission for pre-college study (就学 shugaku, 6 months or 1 year) or college study (留学 ryugaku, 1 or 2 years). Students attending unaccredited institutions, such as many foreign-run schools in Japan, receive landing permission for cultural activities () which is valid for 6 months to 1 year. College students are not initially permitted to work, but may receive permission to work up to 28 hours per week by filing with the Ministry of Justice.
Work permits fall into a number of categories. Most are valid for 1 or 3 years, except for entertainer permits (valid for 3, 6 or 12 months) and diplomatic/NGO permits (valid for duration of post). An employer is generally necessary to serve as the applicant's guarantor; after landing, the applicant may work for any employer within the scope and duration of their landing permission.
Spouses and children
Spouses and dependent children of aliens permitted to land in Japan are given landing permission for the same duration as their spouse/parent.
Spouses and dependent children of Japanese nationals may receive landing permission for 1 or 3 years. Generally, initial landing permission is for one year, and is extended to three years upon the first or second renewal.
Long-term residency is a special class of residency generally granted to refugees, Japanese descendants from overseas, and other particular groups.
Permanent residency (永住権 eijuken) is the strongest form of landing permission, granting the bearer the right to live and work in Japan indefinitely. It must be applied for and obtained within Japan, generally after five to ten years of continuous residency there.
One major advantage of permanent residency is that financial institutions often deny loans to foreigners who are not permanent residents. This practice was upheld as legal in Herman v. Asahi Bank (Tokyo D. Ct. Nov. 12, 2001) .
Once in Japan, aliens must register with the local government office having authority over their place of residence, pursuant to the Alien Registration Law of 1952 . Each registrant is issued a Certificate of Alien Registration, colloquially known as a Gaijin Card, which they are legally required to carry at all times and present upon demand (e.g. by a police officer). The certificate is the property of the Japanese government and must be surrendered at the time the alien leaves Japan, unless they have first applied for re-entry.