Leinster Rugby 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. The team represents the Leinster Branch, one of the four provincial unions that together make up the Irish Rugby Football Union (IRFU), but is not restricted to players from that province.

Leinster play their home games primarily at the 18,500-capacity RDS Arena in Dublin, although larger games are played in the 51,700-capacity Aviva Stadium when the capacity of the RDS is insufficient, or during 2024 and 2025 to accommodate venue improvements at the RDS, with occasional on-off games been moved to Croke Park, home of the Gaelic Athletic Association and by some distance the largest stadium in Ireland. 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 since it was founded in 2001. Before 1995, the Leinster Branch had previously competed in the annual Irish interprovincial championship.

During their professional history, Leinster have been the most successful team in Ireland or from the Celtic League and its successors. As of 2024, Leinster have won their domestic title on eight occasions, while topping the regular season table a further five times, and have won as of 2025 all four URC Irish Shields. In Europe, Leinster are second only to Toulouse with four European Champions Cups, one EPRC Challenge Cup and four runners-up placings in the Champions Cup.

Leinster enjoy historical rivalries with all three provincial unions, most notably with Munster, where some games between the teams have been watched by over 80,000 fans in Croke Park. In addition, Leinster have notable rivalries with two French club teams; erstwhile rivals Toulouse with whom they have jockeyed for the title of Europe's most decorated team, and La Rochelle, a frequent opponent in European competition who defeated Leinster in back to back European Champions Cup finals in 2022 and 2023 under the direction of long-time Munster player Ronan O'Gara.