The Dublin-Rosslare Main Line is a main rail route between Dublin Connolly station and Rosslare Europort, where it connects with ferry services to the United Kingdom and mainland Europe. The line between Dublin and Greystones is electrified and forms the southern part of the DART service. Between Bray and Rosslare the line is single track only. The line connected with the Limerick–Rosslare line outside Rosslare Strand until 2010. From Wicklow on, semaphore signalling was used until April 2008, when the entire line was upgraded to the mini-CTC system controlled from Dublin Connolly. Although it is designated as a separate route, the line is continuous after Dublin Connolly, where it connects with the Belfast–Dublin main line. The section between Westland Row and a point on the line just after Salthill and Monkstown station is the oldest railway line in Ireland, and the first commuter railway in the world, opening in 1834. It was then known as the Dublin & Kingstown Railway. At that time, the railway terminated adjacent to the start of Dún Laoghaire Harbour's West Pier, at a station called Kingstown.

Connolly station or Dublin Connolly is one of the busiest railway stations in Dublin and Ireland, and is a focal point in the Irish route network. On the North side of the River Liffey, it provides InterCity, Enterprise and commuter services to the north, north-west, south-east and south-west. The north–south Dublin Area Rapid Transit (DART) and Luas red line light rail services also pass through the station. The station offices are the headquarters of Irish Rail, Iarnród Éireann. Opened in 1844 as Dublin Station, the ornate facade has a distinctive Italianate tower at its centre.