Quick answer
If one of your passports is from an EU/ETIAS country
Travellers who hold a travel document issued by a participating European country should generally use that document rather than a third-country passport that would require ETIAS. Carrier checks are based on the document presented.
If both passports are non-EU
Choose the passport that gives you the relevant visa-exempt status and that you intend to use for the journey. Apply for ETIAS with that exact travel document.
Present the same document to the carrier
Carrier systems check the travel document presented. If you present a different passport from the one linked to ETIAS, the automated check can return a negative ETIAS result.
Keep your travel-document choice consistent
Use the same passport for application, boarding and border checks wherever possible. If you switch to a new or different travel document, verify whether a new ETIAS is required.
Frequently asked questions
I am American and Italian. Do I need ETIAS?
If you travel using your valid Italian passport under EU free-movement rules, ETIAS is not required.
Can I apply using one passport and travel using the other?
That can create a failed automated ETIAS check because the authorisation is linked to the document used in the application.
What if both passports are ETIAS-eligible?
Use the passport you will actually present for the trip and keep that choice consistent.
Official sources
We use official European Union ETIAS information as the primary source for factual requirements.