The Mourne Mountains, also called the Mournes or Mountains of Mourne, are a granite mountain range in County Down in the south-east of Northern Ireland. They include the highest mountains in Northern Ireland, the highest of which is Slieve Donard at 850 m (2,790 ft). The Mournes are designated an Area of Outstanding Natural Beauty and it has been proposed to make the area Northern Ireland's first national park. The area is partly owned by the National Trust and sees many visitors every year. The Mourne Wall crosses fifteen of the summits and was built to enclose the catchment basin of the Silent Valley and Ben Crom reservoirs.

Granite is a coarse-grained (phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies underground. It is common in the continental crust of Earth, where it is found in igneous intrusions. These range in size from dikes only a few centimeters across to batholiths exposed over hundreds of square kilometers.