The Great Southern and Western Railway (GS&WR) was one of the main railway operations in Ireland in the late 19th and early 20th centuries. The company was the largest of Ireland's "Big Four" railway operators, buying up smaller operations and expanding its route mileage for much of its existence.

The heart of the GS&WR was the Cork-Dublin main line, the "Premier Line", a route still important in Ireland today. William Dargan was the driving force behind this and other GS&WR routes, and he was also responsible for other routes in Ireland not part of the GS&WR. The company's base of operations was Kingsbridge (now Heuston) Station in Dublin. At its height, the GS&WR included, in addition to the Dublin-Cork main line, the Dublin - Waterford and Mallow - Waterford lines as well as numerous branch lines.

Competition:

The GS&WR competed with the Midland Great Western Railway for many years. Both ran services west out of Dublin: the GS&WR's services south to Limerick, Cork and Waterford, with the MGWR running to Galway, Westport, Ballina, and Sligo, all destinations still served by rail. The GS&WR also had designs on rail traffic to the west of Ireland. A branch was built from the Dublin-Cork main line to connect with the MGWR Dublin-Galway line at Athlone. In the end, the GS&WR route was the one chosen many years later by the single rail operator, Córas Iompair Éireann, and is the route used today from Dublin to Galway.

Waterford, Limerick and Western Railway:

The GS&WR's purchase in 1901 of the Waterford, Limerick and Western Railway brought the Waterford - Limerick - Athenry - Claremorris - Collooney cross country route, as well as the North Kerry line and branches under its umbrella. The WLWR, recently dubbed the Western Rail Corridor, ran right through "MGWR territory". It did, however, complement the radial MGWR lines from Dublin, allowing for traffic from Limerick to Galway and from Galway to Sligo, and connected intermediate destinations in the west of Ireland. For a very short time, the MGWR exercised running powers over the Athenry - Limerick section of this route.

GS&WR hotels:

In an effort to encourage tourism the Killarney Junction Railway, which was operated by the GS&WR, opened in 1854 a hotel next to its station in Killarney. In was the first railway-owned hotel in Ireland and one of the first of its kind in the world. In the following years the GS&WR set up further hotels in Kerry at Caragh Lake, Kenmare, Waterville and Parknasilla. In addition the company owned small hotels at Limerick Junction and close to its stations in Dublin and Cork.

In 1925 the hotels became part of Great Southern Hotels, a subsidiary of Great Southern Railways. The Great Southern Hotels Group was dissolved in 2006, when its hotels were sold of separately to private investors.

GS&WR routes today:

The GS&WR is perhaps the best remembered of the former independent rail operators in Ireland's railway history, with GS&WR routes remaining some of the most heavily used in Ireland, connecting Dublin to Limerick, Cork, and Waterford. The coats of arms of these cities decorate the facade of Heuston Station to this day.

Great Southern Railways:

In 1925 the GS&WR was amalgamated with all the other railways operating wholly within the Irish Free State to form the Great Southern Railways. Cross-border railways were excluded from the merger.

Coras Iompair Éireann:

In 1945, further amalgamation with the Grand Canal Co., and the Dublin United Tramway Company brought about the creation of Córas Iompair Éireann, the Irish State Transport Company. CIÉ was nationalised in 1950, only to be broken up into separate rail and road interests in 1987. From then until today, the railways are operated by Irish Rail (Iarnród Eireann).