Leinster House is the seat of the Oireachtas, the parliament of Ireland. Originally, it was the ducal palace of the Dukes of Leinster. Since 1922, it has been a complex of buildings of which the former ducal palace is the core, which house Oireachtas Éireann, its members and staff. The most recognisable part of the complex, and the "public face" of Leinster House continues to be the former ducal palace at the core of the complex.

The Oireachtas, sometimes referred to as Oireachtas Éireann, is the bicameral parliament of Ireland. The Oireachtas consists of the president of Ireland and the two houses of the Oireachtas, a house of representatives called Dáil Éireann and a senate called Seanad Éireann.