This is what we found on Wikipedia regarding the Leinster Rugby:

Leinster Rugby (Irish: Rugbaí Laighean) is one of the four professional provincial club rugby union teams from the island of Ireland. They compete in the United Rugby Championship and the European Rugby Champions Cup.

Leinster play their home games primarily at the RDS Arena, although larger games are played in the Aviva Stadium when the capacity of the RDS is insufficient. Before moving to the RDS in 2005, Leinster's traditional home ground was Donnybrook Stadium, in Dublin 4. The province plays primarily in blue with white or yellow trim and the team crest features a harp within a rugby ball, the harp being an ancient symbol of the province found in and taken from the flag of Leinster, although the traditional colours of Leinster Rugby mean the design more resembles the flag of the president of Ireland or the coat of arms of Ireland.

Leinster turned professional along with its fellow Irish provinces in 1995 and has competed in the United Rugby Championship (formerly known as the Celtic League, Magners League and the Pro12 / Pro14) since it was founded in 2001, having previously competed in the annual Irish interprovincial championship.