Republic of Ireland – United Kingdom border in the context of "Carlingford Lough"

In these lists of mountains in Ireland, those within Northern Ireland, or on the Republic of Ireland – United Kingdom border, are marked with an asterisk, while the rest are within the Republic of Ireland. Where mountains are ranked by height, the definition of the topographical prominence used to classify the mountain (e.g. the change in elevation required between neighbouring mountains), is noted. In British definitions, a height of 600 metres (1,969 ft) is required for a mountain, whereas in Ireland, a lower threshold of 500 metres (1,640 ft) is sometimes advocated.

The lowest minimum prominence threshold of any definition of an Irish mountain is 15 metres (49 ft) (e.g. the Vandeleur-Lynam), however most definitions, including the International Climbing and Mountaineering Federation (UIAA) criteria, do not consider prominences below 30 metres (98 ft) as being mountains (e.g. must at least be an Arderin or a Hewitt). Many British definitions consider a peak with a prominence below 150 metres (492 ft), as being a top, and not a mountain (e.g. must be a Marilyn). A widely used definition of an Irish mountain requires a minimum prominence of 100 metres (328 ft) (e.g. a HuMP), and is the basis for the 100 Highest Irish Mountains.