If you are a British citizen, you do not need a passport to enter Ireland. However, some carriers and airlines might require identification. Irish immigration officers check the ID of all passengers arriving by air from the UK and might ask for proof of British nationality, particularly if you were born outside the UK.

Travel between the UK and Ireland is governed by the Common Travel Area (CTA) agreement, but documentation requirements have tightened recently. As of 2026, while British and Irish citizens do not technically need a passport to cross the border by land or sea, almost all airlines (including Aer Lingus and Ryanair) now mandate a valid passport or an Irish Passport Card for boarding. For non-British or Irish nationals, the rules are stricter: if you are a citizen of a country that requires a UK Electronic Travel Authorisation (ETA), you must ensure your digital permission is linked to your passport before travel. Even when traveling by ferry (e.g., Holyhead to Dublin), you should carry a government-issued photo ID, such as a driving license, though a passport is always the safest and most universally accepted document. If you are a visa-national for either country, you must ensure you have the specific visa required for your destination, as the CTA does not grant automatic visa-free entry for all nationalities.