This one is relevent for me. I was born in the UK in the 70's to a British father and US mother; automatically from this I had British citizenship. My parents then registered me at the US consulate to receive a US birth certificate and allow travel on my mother's passport (they moved back to the US when I was 10 months old). I had also heard the choose citizenship by 18, since I had lived in the US most of my life and had a US passport by that time I didn't think anything of it. However a few years ago I started looking back into dual citizenship as I'd like to work in Europe and having British citizenship would make it easier; everything I had read suggested I could have both passports. I applied and received my British passport (RFID) last year; this involved sending in my British birth certificate and my mother's passport that I left the UK in 1972 on (amazingly she still had it). There's definitely some tricks with laws and tax implications; Britain doesn't require citizens paying taxes on foreign-earned revenue, but the IRS does. You also officially have to enter the US on your US passport and Britain on your British passport.