A common travel area is in existence between Ireland and the UK (including the Channel Islands and the Isle of Man). There is no formal agreement between Ireland and UK regarding the common travel area and it is not provided for in legislation. The first legal recognition of the common travel area between Ireland and the UK is contained in the Treaty of Amsterdam.
The Common Travel Area means that there are no passport controls in operation for Irish and UK citizens travelling between the two countries. Since 1997, some controls are in effect on arrivals in Ireland from the UK but this does not mean that you are required to carry your Irish or UK passport with you when you travel between the countries. You must, however, carry an acceptable form of photo-identification, examples of which are listed below. When you arrive in Ireland, you may sometimes be asked for valid official photo-identification which shows your nationality. As you are being asked to prove that you are an Irish or UK citizen who is entitled to avail of the Common Travel Area arrangements, it would be advisable to travel with your passport.
The Common Travel Area also involves some co-operation on matters relating to immigration issues. A third country national, for example, may be refused permission to enter Ireland if it is his or her intention to travel onwards to the UK and he or she would not qualify for admission to the UK under the Aliens (Amendment) Order 1975.
Irish immigration officers have the power to carry out checks on people arriving in the State from the UK and to refuse them entry to the State on the same grounds as apply to people arriving from outside the Common Travel Area. These checks are carried out selectively.
If you are a citizen of a country whose nationals need a visa to enter Ireland and you have a valid UK visa or residence permit, you may be required to have a valid visa before you arrive in Ireland. The holiday and other short-stay Visa Waiver Programme (pdf) allows nationals of countries such as India, China and the Russian Federation, who have a short-term UK visa to come to Ireland without the need for a separate Irish visa. From autumn 2014, under a new British Irish Visa Scheme, visitors from China and India will be able to travel freely within the Common Travel Area, using either an Irish or UK visa.
If you have a question relating to this topic you can contact the Citizens Information Phone Service on 0761 07 4000 (Monday to Friday, 9am to 8pm) or you can visit your local Citizens Information Centre.