The second Luas line, the Red Line, was officially opened by the Taoiseach, Bertie Ahern, in Dublin today.
Speaking at the launch in Tallaght, Mr Ahern described it as an historic day and said the Light Rail System was a vital component in the Government's transport strategy.
The Red Line, which runs from Connolly Station to Tallaght, is almost double the length of the Sandyford to St Stephen's Green Line and has almost six times as many junctions.
Among the main benefits of the line, which links Connolly and Heuston stations, will be better access to St James's Hospital, and easier commuting to and from the Tallaght area.
There will be six free travel days on the line from this afternoon until the last tram on Sunday, 3 October.
Meanwhile, there was a minor collision involving a Luas tram and a car in Smithfield in Dublin early today.
The tram, which was on a test run at the time, was slightly damaged and was taken out of service. Nobody was injured.
