Glencullen (, meaning valley of the holly) is a village and townland in the county of Dún Laoghaire-Rathdown in south County Dublin, Ireland. It is also the name of the valley above one end of which the village sits, and from which it takes its name, and is on the R116 road, on the slopes of Two Rock Mountain. The highest point of the area is at a height of about , making Glencullen one of the highest villages in Ireland.