The Wicklow Mountains form the largest mountains in Ireland. They fill the whole centre of County Wicklow and stretch outside its borders into Counties Dublin, Wexford and Carlow. Where the mountains extend into County Dublin, they are known locally as the Dublin Mountains.The highest peak is Lugnaquilla at 925 meters.

The mountains are primarily composed of granite surrounded by an envelope of mica-schist and much older rocks such as quartzite. They were pushed up during the Caledonian orogeny at the start of the Devonian period and form part of the Leinster Chain, the largest continuous area of granite in Ireland and Britain. The mountains owe much of their present topography to the effects of the last ice age, which deepened the valleys and created corrie and ribbon lakes. Copper and lead have been the main metals mined in the mountains and a brief gold rush occurred in the 18th century. Several major river systems have their source in the mountains, such as the Liffey, Dargle, Slaney and Avoca rivers.