Leinster ( — — ) is one of the Provinces of Ireland situated in the east of Ireland. It comprises the ancient Kingdoms of Mide, Osraige and Leinster. Following the Norman invasion of Ireland, the historic fifths of Leinster and Mide gradually merged, mainly due to the impact of the Pale, which straddled both, thereby forming the present-day province of Leinster. The ancient kingdoms were shired into a number of counties for administrative and judicial purposes. In later centuries, local government legislation has seen further sub-division of the historic counties.
Leinster has no official function for local government purposes. However, the province is an officially recognised subdivision of Ireland. It is listed on ISO-3166-2 as one of the four provinces of Ireland and "IE-L" is attributed to Leinster as its country sub-division code.
The population of Leinster is 2,504,814 according to the 2011 census, making it the most populous province in the country The traditional flag of Leinster features a golden harp on a green background.