With the arrest of Iranian-American journalist by Iran on charges of spying for the United States, the concept of dual nationality comes into play. Roxana Saberi held both U.S. and Iranian citizenship and while she may have lived in the U.S., Iran claims she is an Iranian citizen and her arrest is a matter of internal affairs.
The concept of dual nationality means that a person is a citizen of two countries at the same time. Each country has its own citizenship laws based on its own policy.Persons may have dual nationality by automatic operation of different laws rather than by choice. For example, a child born in a foreign country to U.S. citizen parents may be both a U.S. citizen and a citizen of the country of birth. U.S. State Department - Dual Nationality.
Dual U.S./Russian nationals who enter Russia on Russian passports face several possible difficulties. Russian authorities will not permit departure from Russia if the person’s Russian passport has expired or has been lost, whether or not the traveler also has a valid U.S. passport. In these cases the traveler will be required to obtain a new Russian passport, a process that can take several months. In order to apply for a Russian visa in a U.S. passport, however, Russian consular officials normally require a person to renounce his or her Russian citizenship.
U.S. citizens also possessing Brazilian nationality cannot be issued Brazilian visas and must obtain a Brazilian passport (from the Brazilian Embassy or Consulate nearest to their place of residence) to enter and depart Brazil. In addition to being subject to all Brazilian laws affecting U.S. citizens, dual nationals may also be subject to other laws that impose special obligations on Brazilian citizens. Note that children adopted from Brazil are still considered Brazilian citizens and must be documented as such should they return to Brazil.