A second passport looks like a purchase. You meet the conditions, pay, receive the document, and the deal feels done.

The obligations attached to citizenship arrive later. Many of them take effect by operation of law, reach your children as readily as you, and only become visible once the moment to act on them has passed.

The rules below span descent, dual nationality, military service, naming, tax, and revocation. None is exotic, and most are already law somewhere a mobile family is likely to hold or claim a passport. Here are 11 that people meet too late.