It’s complicated (in fact, even the distinction between nationality and citizenship can be complicated – we’ll use citizenship here). One of the reasons immigrants delay applying for U.S. citizenship is because they fear they’ll lose their original citizenship. Citizenship is important; it allows you to live and work and more in a country. In the European Union, citizenship of a country means you’re a citizen of the EU which gives you rights in many countries, so that’s not something most people want to lose.
Today countries have become more flexible on allowing dual (or even more) citizenship. If you’re thinking of naturalizing, you want to check the situation in relation to the law of the U.S. and the other country.
The Immigration & Nationality Law of the U.S. says that nationals may lose their U.S. status for certain specific reasons including voluntary naturalization in a foreign country after reaching 18, with the intention to relinquish U.S. nationality. Recently, some U.S. citizens have renounced their citizenship to gain lower tax rates elsewhere. But most U.S. citizens don’t want to give up their U.S. citizenship when they naturalize elsewhere. In that case they can maintain both as long as the other country allows it.
For more information on U.S. policy, see the State Department’s website.
