Cliffs of Moher, Natural cliffs in Liscannor, Ireland.

The Cliffs of Moher run about 14 kilometres along the Atlantic in County Clare, from Hag's Head, where they rise 120 metres, to their highest point of 214 metres just north of O'Brien's Tower. They consist mainly of Namurian shale and sandstone beds, with the oldest rock at the bottom, and a detached rock pillar stands in the water offshore.

The cliffs are named after a promontory fort called Mothar or Moher that stood on Hag's Head. It was demolished in 1808, and its material was used for a lookout tower built against a French invasion during the Napoleonic Wars. O'Brien's Tower, a round stone tower near the midpoint, was built in 1835 by Sir Cornelius O'Brien.

The name comes from the Irish Aillte an Mhothair, after the promontory fort Mothar or Moher that stood on Hag's Head; the fort was demolished in 1808 to build a signal tower. The cliffs have served as a film location, including for Harry Potter and the Half-Blood Prince and Star Wars Episode 7, and in 1994 the Kelly Family shot the cover of their album Over the Hump here.

The visitor center is built into the hillside and offers exhibitions on regional geology and wildlife. The paths along the cliffs are partly paved but can become slippery during strong winds and rain.

The cliffs are not Ireland's highest: Slieve League in County Donegal reaches 601 m and the Croaghaun cliffs on Achill Island 664 m, though neither is developed for visitors. The rock is Namurian shale and sandstone, formed 313 to 326 million years ago as river sediment in an ancient marine basin.