Ireland's first railway opened in 1834 to connect Dublin to its port of Kingstown, now Dún Laoghaire. As in Great Britain, the Irish rail network grew during the 19th century but on a much smaller scale. The terrain was lowland and not difficult to cross, but the population was thinner (especially after the disastrous Famine) and there were fewer industrial customers for freight traffic. In the 1840s the two islands adopted standard gauges for all their tracks but with different widths. Great Britain's was 1435 mm which became the "standard gauge" for many countries, Ireland chose 1600 mm, so its coaches have a little more elbow-room. The mythology arose that GB standard gauge derived from the ruts of Roman chariots. Ireland's gauge happened to match the Diolkos (Δίολκος) by which ships were portaged across the isthmus of Corinth circa 600 BC; scholars have somehow overlooked this toga-wearing epoch of pre-Celtic Ireland.

So north and south Ireland had, and still have, the same gauge, but cross-border transport was blighted in 1921 by partition, and border counties such as Donegal and Monaghan lost their mainline services. The Irish economy also languished, and when that recovered it was the age of the car, with gentlemen of Ireland labouring on road improvement projects across western Europe. Railways received scant investment, though the "Enterprise Train" plied between Dublin and Belfast to attract business travel. In the late 20th century "Troubles" Northern Irish transport was frequently targeted, with murderous attacks and disruptive bomb threats. The Good Friday Agreement of 1998 brought peace and a resumption of leisure rail travel, though car and bus travel grew faster as the motorways developed. Air travel is not a direct competitor within Ireland, but Dublin Airport lacks a railway yet has express buses to all parts of the country.

Trains are diesel (only the Dublin DART network is electrified) and rattle along at up to 160 km/h (100 mph). Dublin - Limerick for instance is only two hours, so there are no plans for TGV-style very high speed lines, and no night trains. There have been few modern changes to the network: Waterford - Wexford was axed, but Limerick - Galway was restored.

Irish Rail or Iarnród Éireann runs all railway services in the Republic of Ireland. It's a subsidiary of Córas Iompair Éireann (CIÉ), a state-owned holding company that also controls the public bus system of Dublin and Bus Éireann, the principal inter-city bus operator.

NI Railways is the state-owned operator of all railway services in Northern Ireland. It's a subsidiary of Translink, whose parent company is the Northern Ireland Transport Holding Company (NITHCo). Translink also operates all public buses in Northern Ireland. The Dublin-Belfast Enterprise Train is jointly run by NIR and Irish Rail.

Also refer to individual city "Get in" sections for more detail. Irish railway stations are small by European and British standards, easy to navigate, and fairly central in town. This section describes all the ports of entry into the Republic and Northern Ireland because they involve a change of transport mode. Dublin, Belfast, Cork and Limerick stations have a couple of points to be aware of. The terminus stations of Waterford, Galway, Westport and Sligo pose no problems and need no further description here. In summary:

• Dublin:

- Dublin Airport (DUB ^IATA) is the Republic's main arrival point. It has no railway (and plans to link it are far from completion), but there's a choice of buses to city centre, including the railway stations. Direct buses run from the airport to all major cities, including Belfast and Derry.

- Dublin ferry port is 2 km east of city centre, take the shuttle bus to Busáras the main bus station. This is next to Connolly railway station.

- Connolly railway station has trains from Belfast via Newry and Drogheda, from Sligo via Longford, from Rosslare ferry port via Wexford and Wicklow, and DART commuter trains.

- Heuston railway station is 4 km west, most conveniently reached by Luas tram. It has trains from Waterford, Cork, Tralee, Limerick, Galway and Westport, with midland stops described below. If you get your ticket made out from Dublin Connolly this includes the tram and saves 50c over separate fares.

• Belfast:

- Belfast City Airport (BHD ^IATA) is 5 km east of the city. Usually you take the bus to city centre, which passes Lanyon Place the main railway station. You could also walk or take the free shuttle bus to Sydenham station, which has suburban trains east to Bangor and west to all Belfast stations, Lisburn and Portadown.

- Belfast International Airport (BFS ^IATA) is 35 km west of the city, with an airport bus. But for Coleraine or Derry take Bus 109A to Antrim railway station from the bus stop outside the terminal building tickets can be purchased for the bus on board the bus then you can purchase train tickets at Antrim train station ticket office if closed purchase from the conductor on board the train.

- Belfast ferry port is 10 km north of city centre, take the shuttle bus to Europa bus station, which is next to Great Victoria Street railway station.

- Lanyon Place is the main station, 1 km east of the centre. All trains run here.

- Great Victoria Street is in city centre next to Europa main bus station. All trains run here except the Belfast - Dublin service.

- Larne ferry port has trains via Carrickfergus to Belfast.

• Rosslare ferry port has trains to Dublin Connolly via Wexford, Wicklow and Bray. The line to Waterford has been axed, take Bus 40 which trundles the width of Ireland to Cork, Killarney and Tralee.

• Cork:

- Cork Airport (ORK ^IATA) is 8 km south of the city, with buses to the centre.

- Cobh is the port for Cork; it has few ferries but lots of cruise ships. The railway station is next to the quay, with frequent suburban trains to the city.

- Suburban trains also run to Midleton (for Jameson Distillery) and Mallow (for Cork racecourse). For Mallow you can also take mainline trains towards Dublin for the same fare.

• Kerry Airport (KIR ^IATA) is midway between Tralee and Killarney. There's a bus, or walk 2 km to Farranfore station for trains.

• Shannon Airport (SNN ^IATA) is 26 km west of Limerick, take the bus to Limerick Colbert bus and railway station.

- to repeat, it's Limerick Colbert for the city. Limerick Junction is 30 km away east on the edge of Tipperary town.

• Knock Airport (NOC ^IATA) is 11 km from the railway stations at Claremorris and Ballyhaunis, both on the Dublin-Athlone-Westport line. And as for the sparse bus service, it'll be a miracle if one happens to come when you need it . . .

• Derry Airport (LDY ^IATA) is within walking distance of the main road, with buses to the city. Derry railway station is across the river 1 km south of the historic city centre.

These radiate from Dublin and Belfast, with only a few side lines or cross-country routes, so it's not so much a network as a star-burst. Frequencies stated are for weekday services — there are fewer on Sunday — and relate to the terminus stations. Trains might flash through a small town hourly but with only a couple per day that stop.

From Dublin Connolly

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To Belfast 8 per day, two hours from Connolly via Drogheda, Dundalk, Newry and Portadown to Belfast Lanyon Place. There are no border checks, long may this remain so, but it's your responsibility to ensure that your documents are valid.

To Rosslare every couple of hours timed for the ferries, 3 hr from Connolly via Dublin Pearse, Dún Laoghaire, Bray, Greystones, Wicklow Town, Rathdrum, Arklow, Gorey, Enniscorthy, Wexford, Rosslare Strand and Rosslare Europort.

To Sligo 7 per day, taking 3 hr 20 min from Connolly via Maynooth, Kilcock, Enfield, Mullingar, Edgeworthstown, Longford, Dromod, Carrick-on-Shannon, Boyle, Ballymote and Collooney to Sligo.

DART suburban trains also run along the coast to Connolly and don't serve Heuston. See Dublin#Get around: you might use them to explore the coast south to Dún Laoghaire, Dalkey and Bray, or north to Malahide and Howth.

At the station: Irish stations are small by European standards, so they're easy to navigate. They all have ticket machines; mainline stations have ticket offices usually open M-F for the morning get-away but smaller places roll down the shutters by mid-afternoon. Toilets are usually accessible during ticket office hours. There may be a vending machine, seldom a cafe or newsagent but most stations are close to town amenities.

Outside the capitals there are generally just one or two platforms. Most stations have step-free access and wheelchair ramps for boarding, but two or three places are problematic: in 2021 Irish Rail are fitting lifts to those stations still needing them. Platforms are displayed on screens 10 min before departures - station and on-train announcements and displays in the Republic are in English and Gaelic. So now you'll find out where on earth is Tiobraid Árann (hint: it's a long way to go).

In 1966, to mark the fiftieth anniversary of the Easter Rising in Dublin, many stations in the Republic were re-named for those executed in its aftermath. So there was damned-nearly a station called "Countess Markievicz née Constance Gore-Booth" but the British commuted her death sentence to life imprisonment, and after a year she was released in a general amnesty.

On the trains: all nowadays have push-button doors that close and lock automatically before departure, and the old slam-door coaches have been retired. All trains have free wi-fi.

Seat reservations are marked either with paper tags on the headrest or an electronic display above the window.

Bicycles must be booked on Inter-city services. Trains from Dublin to Cork and Belfast have dedicated space. Others share the passenger space, which can only fit a couple of standard bikes (up to 1.8 m long and 0.865 m wide), so no tandems, trikes, trailers or club outings. On Commuter or Dart trains, which have no booking, fold-up bikes can be carried any time but standard bikes are not allowed during M-F rush hour.

First Class is only available on the Dublin-Belfast Enterprise train; normally also Dublin-Cork but this is suspended in 2021, as is on-train catering in the Republic. Northern Ireland doesn't have either apart from the Dublin route.

Trains are safe and comfortable, with slightly more elbow-room than in Great Britain or the Continent. Keep your ticket and any pass with you when you move about the train as you may be asked to show it.

Ireland's railways were built in the Victorian age like Great Britain's, but the unique gauge and small network means there isn't the same wealth of heritage. There are no tourist trains, and Britannia or Tornado are never going to halt with a gush of steam at Drogheda, or disgorge 50 blazers and straw trilbies at Killarney. Pity. Many local museums have a section depicting their railway, since it was part of the town's development. The only working "heritage" line in the Republic is modern, a narrow-gauge railway laid over an abandoned standard-gauge track-bed near Waterford. There are a few small railway museums, sometimes in steam, for instance at Dromod and Castlerea. Model railways run at Malahide near Dublin and Clonakilty in County Cork.

It can be no accident that the best displays are in Northern Ireland. When loyalists wave the Union flag, they assert their British birthright to be obsessive about ramshackle old steam locomotives. The Ulster Transport Museum in Holywood is a fine example (and you can get there by train, heading from Belfast to Bangor, get off at Cultra). There are two tracks you can ride: from Bushmills to Giant's Causeway, and from Downpatrick to the ruined abbey. One railway enthusiast spent much money and effort on preserving the Downpatrick locos, as he'd been assured (correctly) that they were standard gauge. It was some years before he twigged that they were Irish standard gauge and couldn't run on his British heritage track.

• Ferry routes to Great Britain - if you don't fly to Ireland then you come by boat, most likely via Great Britain.
• Rail travel in Great Britain - rail travel on the other big island.