http://www.richw.org/dualcit/law.html#LossCitLoss of citizenship (INA § 349, 8 USC § 1481)
Section 349 of the INA <8 USC § 1481> specifies several conditions under which US citizenship may be lost. These include:
* becoming a naturalized citizen of another country, or declaring allegiance to another country, after reaching age 18;
* serving as an officer in a foreign country's military service, or serving in the armed forces of a country which is engaged in hostilities against the US;
* working for a foreign government (e.g., in political office or as a civil servant);
* formally renouncing one's US citizenship before duly authorized US officials; or
* committing treason against, or attempting or conspiring to overthrow the government of, the US.
The primary effect of recent developments in the US regarding dual citizenship has been to add the requirement that loss of citizenship can only result when the person in question intended to give up his citizenship. At one time, the mere performance of the above (or certain other) acts was enough to cause loss of US citizenship; however, the Supreme Court overturned this concept in the Afroyim and Terrazas cases, and Congress amended the law in 1986 to require that loss of citizenship would result only when a potentially "expatriating" (citizenship-losing) action was performed voluntarily and "with the intention of relinquishing United States nationality".
On 16 April 1990, the State Department adopted a new policy on dual citizenship, under which US citizens who perform one of the potentially expatriating acts listed above are normally presumed not to have done so with intent to give up US citizenship. Thus, the overwhelming majority of loss-of-citizenship cases nowadays will involve people who have explicitly indicated to US consular officials that they want to give up their US citizenship.