MacGillycuddy's Reeks (Irish: Na Cruacha Dubha, meaning 'the black stacks') is a sandstone and siltstone mountain range in the Iveragh Peninsula in County Kerry, Ireland.

The rocks date from the Upper Devonian period (310–450 million years ago) when Ireland was in a hot equatorial setting.

[9][5] Only two of the eleven Reeks over 3,000 ft meet the Marilyn classification of a mountain (a prominence above 150 metres), namely Carrauntoohil and Cnoc na Péiste.

[2][3] In 2019 the Irish Times reported that the MacGillycuddy Reeks Mountain Access Forum, a cross-body group of landowners, commercial users and public access and walking groups set up in 2014 with the aim of "protecting, managing and sustainably developing the MacGillycuddy's Reeks mountain range, while halting and reversing the obvious and worsening path erosion", had achieved some success laying down new pathways in the Hag's Glen approach to Carrauntoohil; however, the Irish Times still wondered, "Should the Kerry reeks be a national park?".

[3] The full name of the range in Irish is Cruacha Dubha Mhic Giolla Mo Chuda, meaning "the black stacks of McGillycuddy".

[14] The MacGillycuddys (Irish: Mhic Giolla Mo Chuda) were a sept, or branch, of the O'Sullivan Moore clan.

The MacGillycuddy is recorded as being one of a smaller number of Gaelic chieftains whose lands were returned post the Cromwellian confiscations, which explains why the name survives to this day.

[3] The Reeks are a popular subject for artists and photographers, with souvenir prints offered for sale among "Views of Ireland.

The popular route starts from Cronin's Yard (V837873) and enters the Hag's Glen to climb the Devil's Ladder (the col between Carrauntoohil and Cnoc na Toinne), from which the summit is accessed.

The most challenging route is the full MacGillycuddy's Reeks Ridge Walk, a 12- to 14-hour, 26-kilometre (16 mi) traverse of the entire range.

The 450 metres (1,480 ft) rock climbing grade Very Difficult (V-Diff), Howling Ridge up the central arete between the east and north-east faces of Carrauntoohil is notable.