Dual citizenship and US law

Yes, you can be a US citizen and a citizen of another country at the same time. Uncle Sam doesn't make you pick a team, but he does set a few ground rules every dual national should know.

The short version

US law allows dual nationality. You don't need US permission to take another citizenship, and doing so doesn't by itself put your US citizenship at risk [1].
You must enter and leave the US on a US passport. This applies to dual nationals too [1][2].
US consular help may be limited in the country of your other nationality, which may treat you only as its own citizen [2].
Foreign military service rarely costs you US citizenship. It only matters if it's voluntary and meant to give up US nationality, or in narrow cases like serving as an officer or fighting against the US [3].
Every US obligation still applies: tax returns, FBAR, Selective Service for men 18 through 25, and jury summonses if you keep a US address [4][5].

What US law actually says

The State Department's page on dual nationality is short and refreshingly plain. A person can be a national of two countries at once. US law doesn't require citizens to ask a court or agency for permission to acquire a foreign nationality, and it doesn't make them choose one or the other [1]. Naturalizing in another country doesn't, by itself, endanger your US citizenship [1].

The government's own manual for consular officers, the Foreign Affairs Manual, puts it this way: the US recognizes dual nationality but doesn't encourage it, because it can complicate diplomatic and consular protection [2].

How people end up with two citizenships

How it happens	Example	Does the US care?
Born in the US to foreign parents	A child born in Texas to Irish parents may also be Irish	No, you're a US citizen by birth
Born abroad to a US citizen parent	A child born in Tokyo to an American mother, registered with a CRBA	No, the CRBA documents US citizenship
Citizenship by descent	An American who claims Italian citizenship through a grandparent	No, US citizenship stays
Naturalizing abroad	An American living in Canada who becomes Canadian	No, as long as you don't intend to give up US citizenship
Becoming American as an adult	A German who naturalizes in the US	The US doesn't care, but Germany's own law decides whether you stay German

Pay attention to that last row. Each country sets its own nationality law [1]. Some countries end your citizenship when you naturalize somewhere else, others need a permit to keep it, and some never let you go. Taking the US naturalization oath doesn't end another country's claim on you under its law [2]. Check the other country's rules with its embassy before you raise your hand at a US naturalization ceremony.

Entering and leaving the US: use your US passport

US citizens, including dual nationals, must use a US passport to enter and leave the United States, under 8 U.S.C. 1185(b) and 22 CFR 53.1, with limited exceptions [1][2]. In practice:

Fly to the US on your US passport. Show it at check-in and to US Customs and Border Protection.
Use your other passport for your other country. That country may require you to enter and leave on its passport [1].
Use either passport for third countries. Traveling to a third country on your foreign passport isn't inconsistent with US law [1]. Pick whichever gives easier entry.
Don't apply for an ESTA or US visa. US citizens aren't eligible for either, and applying on your foreign passport can cause trouble at the border.
Keep your US passport valid. If it expires while you're abroad, renew it before your trip. Our guide to renewing a US passport abroad covers the online and mail options.

A common mistake is booking a flight on the foreign passport and then showing the US one at the airport. Airlines check that the passport matches the booking, so book with the passport you'll show at departure, or make sure the names match exactly. It's a small thing that can turn a smooth trip home for Thanksgiving into a long morning at the check-in desk.

If your second passport is Australian, our sister site ExpatCooee explains renewing an Australian passport from overseas, so you can keep both books current.

Consular help in your other country

If you live in the country of your other nationality, that country generally has the stronger claim on you while you're there [2]. It may treat you only as its citizen, even if you entered on a US passport [2].

That has real-world consequences:

Arrest: under the Vienna Convention on Consular Relations, a host country usually doesn't have to notify the US embassy when it detains someone who is also its own citizen [2]. Some bilateral agreements set different rules.
Exit bans: a country can stop its own citizens from leaving, for example over a court case or unpaid debts, and the US embassy may have little leverage.
Family law: child custody, divorce and inheritance follow local law for local citizens.

The State Department's travel advisories flag countries where dual nationals face specific risks. Enroll in STEP so the embassy can reach you, and read the advisory for your other country before you travel there. Our guide to STEP and help from US embassies explains what embassies can and can't do.

Military service

Some countries require military service from their citizens, and dual nationals living there may be called up. The US doesn't stop you from serving, and compulsory service in a country where you live or are a citizen isn't, by itself, a reason to lose US citizenship [3].

Under section 349(a)(3) of the Immigration and Nationality Act, foreign military service can lead to loss of US nationality only if it's voluntary and done with the intention of giving up US citizenship [3]. The State Department notes two situations where service is more serious [3]:

serving as an officer in a foreign military
serving in the forces of a country engaged in hostilities against the United States

Even then, the person must have acted voluntarily, and loss isn't automatic. Each case turns on its own facts [3]. Separate federal laws restrict recruiting for foreign forces inside the US [3].

Selective Service

US citizen men must register with the Selective Service System from age 18 through 25, wherever they live. That includes dual nationals, and Selective Service has a foreign-address registration form for men abroad [5]. Failing to register can bar you from some federal jobs later, so don't skip it. Our guide to jury duty, Selective Service and other obligations from abroad covers the details.

What a second passport doesn't change

Holding another passport doesn't get you off the hook stateside. The US taxes citizens on worldwide income wherever they live [4]. So a dual citizen living in their other country still:

files a US federal tax return, with the automatic extension to June 15 for people living abroad [4]
reports foreign bank accounts on the FBAR (FinCEN Form 114) once the total tops $10,000 at any time in the year
may file Form 8938 for foreign financial assets above the higher thresholds for people abroad
can vote in US federal elections by absentee ballot

Many "accidental Americans", people born in the US who left as children, first discover these rules when a foreign bank asks for a US tax number under FATCA. If that's you, our guide to catching up on missed returns explains the Streamlined procedures. A US expat tax preparer (or lawyer) can check your situation.

The only way to end these duties is to give up US citizenship formally at a US embassy or consulate, which has its own costs and possible exit tax. It's a big, permanent step, not a paperwork shortcut.

A quick checklist for dual nationals

Keep both passports valid, and renew the US one before it lapses.
Book US flights on your US passport.
Check your other country's rules on entry, exit and military service.
Register with STEP and read the advisory for your other country.
Register with Selective Service if you're a man aged 18 to 25.
File your US tax return and FBAR every year.
Register children born abroad with a CRBA so their US citizenship is documented.

You can swap experiences with other dual citizens in our community groups for Americans abroad.

Dual citizenship and US law: two passports, one set of US rules