What to do with the first passport after acquiring a second

After acquiring a second nationality there are three options for the first, and most people take the third by default without noticing they have decided anything.

Keep it

The default where both countries permit dual nationality, and usually correct. A citizenship is an unconditional right of entry and residence somewhere, and that is worth holding even when it is not used.

• Keep the passport valid. An expired passport is not a lost citizenship, but renewing after a long lapse from abroad is slower than renewing on time.
• Continue meeting any obligations attached — notification, registration, filings.
• Remember it still counts for compliance and screening wherever you bank.

Renounce it

A formal procedure, not a decision you make privately.

• Most countries will not permit renunciation that would leave you stateless, so another citizenship must already be held.
• Some will not permit it while obligations are outstanding — military service being the usual one.
• It is generally irreversible and removes your right to enter and live in that country.
• It may trigger a tax charge. One country imposes an expatriation tax on people above defined thresholds, and that is planned for years in advance rather than at the moment of decision.
• Some countries require a fee and an interview; a few make it deliberately difficult.

Let it lapse

The default, and it is not a neutral option. An expired passport still means you are a citizen, with the obligations that carries and none of the convenience. It also creates a practical problem: countries that require their citizens to enter on their own passport will not admit you on the other one, and you cannot obtain the first quickly from abroad.

The question that decides it

Would you ever need to live in that country again — for care, for family, for a change of circumstances? If the answer is possibly, keep it. Renunciation should be reserved for cases where the first citizenship carries an obligation you genuinely cannot accept, and it should be taken with tax advice rather than emotion.