From Great Britain And Northern Ireland
Due to ROI's long relationship with the UK, there are no permanent passport controls at land border crossing points. In fact, the border is rarely signposted and it is often difficult to tell when you have crossed from the Republic into the Northern Ireland and vice-versa. The most obvious signal is that the roadsigns on the Republic side are mostly bilingual, in Irish and English, and speed limits and distances are shown in kilometres. You may also notice changes in lines in the road; yellow thick lines in the south and white thin lines in Northern Ireland. When arriving at an Irish airport from Great Britain, you will be required to produce photo ID driver's licence or passport to prove that you are a British or Irish citizen. EU/EEA nationals do not need passports for travel between the two, but all other foreign nationals need a passport.
However, despite the lack of border controls, be keenly aware that you must possess a valid Irish visa if required for your nationality, or you risk being deported for illegal presence in Ireland. It is not uncommon that the Irish police An Garda Siochána check passports at the border occasionally - especially when traveling by bus or train.
If you are flying with Ryanair (http://www.ryanair.com/en...) - into Ireland from the UK you must be in possession of passport or equivalent national identity card. Ryanair will not accept a driver's licence although Irish Immigration GNIB do.
By plane
The Republic of Ireland is served by 4 international airports, Dublin IATA: DUB, Shannon IATA: SNN in County Clare, Cork IATA: ORK and Ireland West, Knock IATA: NOC in County Mayo. Dublin, the 8th largest airport in Europe, is by far the largest and most connected airport, with flights to many cities in the US, Canada, the UK, continental Europe and the Middle East. Shannon, close to the city of Limerick, also has flights to the US, Canada, Middle East, the UK and Europe. Cork has flights to most UK destinations and a wide variety of European cities. It is easily accessed from any of the major European hubs, including all of the London airports. Knock Airport has daily scheduled flights to several UK cities, as well as various chartered flights to mostly holiday destinations in Europe.
Smaller regional airports that operate domestic and UK services include Donegal IATA: CFN, Galway IATA: GWY, Kerry IATA: KIR, Sligo IATA: SXL and Waterford IATA: WAT.
The City of Derry Airport, and both Belfast airports both the City and International are within a relatively short distance from the North/South border, especially the former. These three airports being located within Northern Ireland.
Ireland's two major airlines Aer Lingus (http://www.aerlingus.com) and Ryanair (http://www.ryanair.com) are low cost carriers. This means that passengers will be charged for every extra including airport check-in Ryanair only, checking in baggage, food onboard, etc. Ryanair also charge for the privilege of being one of the first to board the plane. Comprehensive listings of airlines flying directly into Ireland, along with destinations and timetables, can be found on the Dublin, Shannon, Cork and Knock airport websites. A regional service is also provided by Aer Arann (http://www.aerarann.ie/) which provides domestic flights within Ireland and international flights mainly to and from the United Kingdom.
Visa Requirements
Ireland is a member of the European Union, but not a member of the Schengen Area. Therefore, separate immigration controls are maintained. The following rules generally apply:
Citizens of EU and EEA countries and Switzerland only require a valid national identity card or passport and do not require a visa for entry or employment; in many cases, the hold unlimited rights to employment and residence in Ireland.
Citizens of Andorra, Antigua & Barbuda, Argentina, Australia, the Bahamas, Barbados, Belize, Bolivia, Botswana, Brazil, Brunei, Canada, Chile, Costa Rica, Croatia, Dominica, El Salvador, Fiji, Grenada, Guatemala, Guyana, Honduras, Hong Kong SAR, Israel, Japan, Kirbati, Lesotho, Macao SAR, Malawi, Malaysia, the Maldives, Mauritius, Mexico, Monaco, Nauru, New Zealand, Nicaragua, Panama, Paraguay, St. Kitts and Nevis, St. Lucia, St. Vincent and the Grenadines, Samoa, San Marino, the Seychelles, Singapore, the Solomon Islands, South Africa, South Korea, Swaziland, Taiwan, Tonga, Trinidad & Tobago, Tuvalu, the United States, Uruguay, Vanuatu, the Vatican City and Venezuela, plus British Nationals Overseas, require valid passports for entry, but they do not need visas for stays not exceeding three months in length. The period of admission is determined by the Immigration Officer at the port of entry, but can be extended up to the full 90 days if required. Foreigners who enter without a visa can also extend this stay after entry, but within the initial period of admission and with a valid purpose. Longer stays, employment, and citizens of other countries normally require advance visas.
Citizens of other countries should check the visas lists (http://www.dfa.ie/home/in...) at the Irish Dept. of Foreign Affairs (http://www.dfa.ie). The visa application process for tourist visas is reasonably straightforward and is detailed on the Irish Naturalisation and Immigration Service website (http://www.inis.gov.ie/en...). Stays based on tourist visas cannot be extended past 90 days under any circumstances.
Because of an informal agreement between the United Kingdom and Ireland, known as The Common Travel Area, there are no passport controls in effect for UK citizens travelling to Ireland. On arriving in an Irish airport from the UK, however, you will be asked for valid official photo-identification such as a passport or driving licence which shows your nationality. This is to prove you are an Irish, UK, or EU citizen who is entitled to avail of the Common Travel Area arrangements. Immigration controls are mandatory on all inbound flights, selective on ferries, and occasional at the land border crossings.
The Common Travel Area and You
If you cross into Ireland by land after arriving in the United Kingdom and being stamped to enter the UK, you will go through passport control at your port of entry into the UK, but you likely will not be required to clear Irish immigration controls, and your authorized stay will generally be under the conditions of your admission to the UK. If you are transiting to Ireland through the UK, however, you will be required to clear passport control in the UK, even if travelling by air. Even if you clear immigration in Ireland, however, after arriving from the UK, this does not count as interrupting your stay in the UK and, accordingly, time spend in Ireland will count against the time you were admitted to the UK.
If you intend to travel to the UK from Ireland, even in transit, you will clear passport control in Ireland, but you will not go through Immigration on arrival in the UK. However, your stay will be limited to a maximum of three months, not six. If you intend to stay in the UK for longer than three months, especially as a Student Visitor in the UK, you must apply to extend your stay in the UK approximately GB£500, obtain a visa for the UK in advance, go to mainland Europe and re-enter the UK, or avoid a transit through Ireland.
However, if you require a visa for either Ireland or the UK, however, you must possess a visa from each country that requires you to have one if you intend to visit both of them. Not passing through passport control does not exempt one from having a visa if needed, and you can be fined and deported for not having a visa if discovered.
By ship
Ireland is served by numerous services from Great Britain and France:
Norfolkline (http://www.norfolkline.com/) - operate freight and passenger services from Liverpool to Dublin.
Irish Ferries (http://www.irishferries.com/) travel from Holyhead, North Wales, to Dublin, and from Pembroke, South Wales, to Rosslare.
Stena Line (http://www.stenaline.com/) connects Holyhead to Dún Laoghaire Co. Dublin about 8 km south of Dublin city centre, and Fishguard, South Wales, to Rosslare.
Irish Ferries and Brittany Ferries (http://www.brittany-ferri...) provide services from France e.g. Roscoff to Rosslare and Cork. Irish Ferries is sometimes significantly cheaper than Brittany Ferries, so compare prices.
Irish Sea Express - Liverpool to Dublin
P&O Irish Sea - north-west England to Dublin
Steam Packet Company - Operate services between north-west England mainly Liverpool to Dublin, and Isle of Man to Dublin.
Fastnet Line (http://www.fastnetline.com/) provide a daily service from Swansea in South Wales to Cork. Currently suspended, this service will resume in March 2010. The service ran previously as Swansea Cork Ferries (http://www.swanseacorkfer...) which no longer operates.
Celtic Link (http://www.celticlinkferr...) Ferries operate the route from Rosslare to Cherbourg which was previously run by P&O Irish Sea.
Numerous companies now act as agents for the various ferry companies much like Expedia and Travelocity act as agents for airlines allowing the comparison of various companies and routes. Three well known brands are Ferryonline (http://www.ferryonline.co.uk), AFerry (http://www.aferry.co.uk/f...) and FerrySavers (http://www.ferrysavers.com/).
By train
The only cross-border train is the Enterprise service jointly run by Irish Rail (http://www.irishrail.ie) and Northern Ireland Railways (http://www.nirailways.co.uk) from Belfast Central to Dublin Connolly.
A Rail-Sail Scheme is also available, linking Stena Line (http://www.stenaline.ie) or Irish Ferries (http://www.irishferries.com) Ferry companies with Train Companies in Great Britain and Ireland. They mainly operate from UK cities across the various Irish and British Rail Network via the Dublin-Holyhead, Rosslare-Fishguard and Rosslare-Pembroke sailing routes.
By bus
Cross border services are operated by Ulsterbus (http://www.ulsterbus.co.uk/) and Bus Ãireann (http://www.buseireann.ie/), and various privately-owned companies servicing County Donegal.
Eurolines (http://www.eurolines.com/) operate services to Great Britain and beyond in conjunction with Bus Eireann and National Express Great Britain. Bus Ãireann also operates frequent services to and from Eastern Europe, in particular Poland, Lithuania, Latvia and Estonia. Additional private travel options are available from Eirebus (http://www.eirebus.ie/) who offer car and coach travel for individuals and group transfers.