US Dual Citizenship: The U.S. government allows dual citizenship. United States law recognizes U.S. Dual Citizenship, but the U.S. government does not encourage it is as a matter of policy due to the problems that may arise from it. It is important to understand that a foreign citizen does NOT lose his or her citizenship when becoming a U.S. citizen. An individual that becomes a U.S. citizen through naturalization may keep his or her original citizenship. However, as some countries do not recognize dual citizenship, it is important to consider it carefully before applying for U.S. citizenship.
Dual citizenship is a complex issue and it is important to understand that there are not only benefits but also obligations that comes with being a dual citizen. Being a citizen of two countries means that you need to obey the laws of both countries, which may include paying taxes and serving in the military. The "United States Dual Citizenship Guide" explains these issues in detail.