The Great Book of Lecan or simply Book of Lecan (Irish: Leabhar (Mór) Leacáin) (RIA, Ms. 23 P 2) is a late-medieval Irish manuscript written between 1397 and 1418 in Castle Forbes, Lecan (Lackan, Leckan; Irish Leacán), in the territory of Tír Fhíacrach, near modern Enniscrone, County Sligo. It is in the possession of the Royal Irish Academy. Nollaig Ó Muraile dated it to c. 1397–1432 or possibly even a little later. Another estimate dated it to the early 15th century.
Leabhar Mór Leacáin is written in Middle Irish and was created by Ádhamh Ó Cuirnín, Murchadh Ó Cuindlis, and an anonymous third scribe for Giolla Íosa Mór Mac Fhirbhisigh. The material within was transcribed from the Book of Leinster, latter copies of the Book of Invasions, the Dinsenchas, the Banshenchas, and the Book of Rights.
