Mingulay (Scottish Gaelic: Miughalaigh) is the second largest of the Bishop's Isles in the Outer Hebrides of Scotland. Located 12 nautical miles (22 kilometres) south of Barra, it is known for an extensive Gaelic oral tradition incorporating folklore, song and stories and its important seabird populations, including puffins, black-legged kittiwakes, and razorbills, which nest in the sea-cliffs, amongst the highest in the British Isles.

There are Iron Age remains, and the culture of the island was influenced by early Christianity and the Vikings. Between the 15th and 19th centuries Mingulay was part of the lands of Clan MacNeil of Barra, but subsequently suffered at the hands of absentee landlords.

After two thousand years or more of continuous habitation, the island was abandoned by its Gaelic-speaking residents in 1912 and has remained uninhabited since. It is no longer used for grazing sheep. The island is also associated with the "Mingulay Boat Song", although that was composed in 1938. The National Trust for Scotland has owned Mingulay since 2000.

In the Pleistocene era Mingulay was covered by the ice sheets which spread from Scotland out into the Atlantic Ocean beyond the Outer Hebrides. After the last retreat of the ice around 20,000 years ago, sea levels were lower than at present and circa 14,000 BP it was joined to a single large island comprising most of what is now the Outer Hebrides. Steadily rising sea levels since that time then isolated the island, which is made up of Hebridean gneiss interspersed with some granite. The ice deposited both erratic blocks of rock and boulder clay on the eastern side of the island around Mingulay Bay. The rest of the island is covered in peat, thin acidic soils, or bare rock.

Mingulay is part of the small archipelago known as the Bishop or Barra Isles which are "composed of a cluster of islands surrounded by a boisterous sea, making the passage of one island to another a matter of very considerable hazard" and which form the southern end of the larger Outer Hebrides group.

There is one large beach on the eastern side of the isle, where the only settlement of note ('The Village') was located, and a tiny cove at Skipsdale (Old Norse: ship valley). Bagh na h-Aoineig (Scots Gaelic: bay of the steep promontory) on the western side is a deep cleft in the sea-cliffs once thought to be the highest in the UK which rise to 213 m (699 ft) above sea level at Builacraig.

Mingulay has three large sea stacks: Arnamul (Old Norse: Erne mound), Lianamul (Old Norse: Flax mound) and Gunamul, which has a natural arch in 150 m (490 ft) cliffs through which boats can sail on rare days when the sea is calm. There are several outlying islets including the twin rocks of Sròn a Dùin to the south-west, Geirum Mòr and Geirum Beag to the south between Mingulay and the nearby island of Berneray, and Solon Mòr ('Big Gannet'), Solon Beag ('Little Gannet'), Sgeirean nan Uibhein, Barnacle Rock and a smaller stack called The Red Boy, all to the north between Mingulay and Pabbay.

The highest hills are Càrnan (273 m or 896 ft), Hecla (Old Norse: Hooded shroud) (219 m or 719 ft) and Macphee's Hill (224 m or 735 ft). The last was named when a relief ship was sent by MacNeil of Barra to discover why communications from the island had ceased. A crewman called Macphee was sent ashore and returned to report that the residents had all died of disease. Fearing the plague, his shipmates refused to allow him back on board. He survived for a year, and climbed the hill every day to look out for a rescue. When the island was re-settled the chief of the Clan MacNeil of Barra granted him land there.