I'm not too familiar with Form 2555, but I'm not aware of a need to indicate dual citizenship.  Maybe I'm wrong?

It is likely our expert in foreign matters will stop by in a while, but in the meantime maybe you can clarify why there is a need to report dual citizenship.  Are you just trying to claim the Bona Fide Residency?

There is no input for dual citizenship.  You will just use USA as the default.

In the event you are trying to claim treaty benefits, you will need to take a consistent position.  US citizens are subject to the Saving Clause.  Your client can't be tax residents of both the US and another state; Article 4 has a pecking order to resolve that.

Thank you.  I ended up figuring this out, and it is good to have colleague feedback confirmation.

What if one of the partners is not a US citizen. How can I enter his county of citizenship that?

Partners on a 2555?

No. I was generally asking for 1065. There is no place to choose the country of citizenship.

@Babak Start a new thread for your question.