There is plenty of confusion on the net about the US allowing dual nationality. According to the US government itself, it does ! Here are some relevant excerpts from the
US State Department web site :

- U.S. law does not mention dual nationality or require a person to choose one citizenship or another.
- The U.S. Government recognizes that dual nationality exists but does not encourage it as a matter of policy because of the problems it may cause.
- A U.S. citizen may acquire foreign citizenship by marriage, a person naturalized as a U.S. citizen may not lose the citizenship of the country of birth.

But here is the complication:

- Most U.S. citizens, including dual nationals, must use a U.S. passport to enter and leave the United States

My question is how to actually do this in practice ? As I was departing the US, because I had a 1-way tickets, the airline in the US insisted on entering details from my NZ passport (because I did not have a NZ entry visa in my US passport that I tried to use first). The airline check-in counter seems to be the only form of departure passport control in the US and I wonder if that information is linked to government data bases ? So, now I planning a business trip from NZ back to the US. I will carry both passports with me, but, apart from the obvious (re-enter NZ with NZ passport) which passport to use when ? In particular on the return leg back to NZ, I suspect that the airline will want to use the NZ passport again.

A search shows conflicting advice in this thread, eg:

Quote Originally Posted by James 1077 View Post
Flying to NZ - show your NZ passport all the way.

Flying to US - show your US passport all the way.

Although if you have both on you then it doesn't matter as you can show both and let the airline decide!
Quote Originally Posted by Hagabel View Post
I have US and UK passports and as a US citizen you have to leave and enter the US on the US passport. That is what I have been told twice by INS.
I leave US on US passport, enter UK on UK passport, leave UK on UK passport and reenter US on US passport. I have shown both to the US airline on leaving the Uk and had no problems at either end.
I applied for PR as a US citizen as I am living in this country. Gets kind of confusing!
Good luck.

and my situation is a little different. I am already in NZ and planning on visiting the US. Any advice on do's and don'ts, especially from dual US/NZ citizens who have been there and done that would be greatly appreciated.

Brent