Leinster is one of the Provinces of Ireland. It lies in the east of Ireland and comprises the counties of Carlow, Dublin, Kildare, Kilkenny, Laois, Longford, Louth, Meath, Offaly, Westmeath, Wexford and Wicklow. Leinster has the largest population of the four provinces of Ireland. The traditional flag of Leinster features a golden harp on a green background.

The only official city in Leinster is Dublin, the capital of Ireland. However, the Greater Dublin Area (GDA) has a total population of 1,661,185 (2006) with some of its larger urban areas comprising the towns of Tallaght & environs, Blanchardstown, Clondalkin and Lucan. The city of Kilkenny (and environs) also has a sizeable population, but is not usually included as a city, despite holding that title for the past 400 years.