Traveling from the UK to Dublin falls under the Common Travel Area (CTA) agreement, which means there are no formal passport controls for British or Irish citizens. However, you still need "valid photo ID" to satisfy airline security and boarding requirements. For British citizens, a valid passport is the most widely accepted and recommended form of ID. Most airlines (including Ryanair and Aer Lingus) specify a passport or a formal Driving License as acceptable. However, you should be extremely careful: while the CTA allows for a driving license, some airlines have internal policies that are stricter than government regulations. If you are not a British or Irish citizen, you must carry a valid passport and, depending on your nationality, you may also require a visa for Ireland, as the CTA does not grant the same rights to all residents. For 2026 travelers, it is also highly recommended to carry a GHIC (Global Health Insurance Card), which ensures you can access necessary healthcare in Ireland just as you would in the UK.