The Great Orme (Welsh: Y Gogarth) is a limestone headland on the north coast of Wales, north-west of the town of Llandudno. Referred to as Cyngreawdr Fynydd by the 12th-century poet Gwalchmai ap Meilyr, its English name derives from the Old Norse word for sea serpent. The Little Orme, a smaller but very similar limestone headland, is on the eastern side of Llandudno Bay. The headland is a tourist attraction, with a Victorian tramway, a cableway, walking routes and a mining museum.

Both the Great and Little Ormes have been etymologically linked to the Old Norse words urm or orm that mean sea serpent (English worm is a cognate). One explanation is that the Great Orme is the head, with its body being the land between the Great and Little Ormes, whilst another, possibly more likely, is that the shape of the Great Orme viewed as one enters the isthmus of Llandudno from the southeast landward end resembles a giant sleeping creature. The Vikings left no written texts of their time in North Wales although they certainly raided the area. They did not found any permanent settlements, unlike on the Wirral Peninsula, but some Norse names remain in use in the former Kingdom of Gwynedd (such as Point of Ayr near Talacre).

Despite there being a theory for the origin of the name "Orme", the word was not commonly used until after the creation of the Victorian resort of Llandudno in the mid-19th century. Before this, Welsh names were predominantly used locally and in cartography to name the headland's landward features and the surrounding area. The entire peninsula on which Llandudno was built was known as the Creuddyn (the medieval name of the cwmwd – a historical division of land in Wales); the headland itself was called Y Gogarth or Pen y Gogarth; its promontories were Pen trwyn, Llech, and Trwyn y Gogarth.

Orme only appears to have been applied to the headland as seen from the sea. In 1748, the Plan of the Bay & Harbour of Conway in Caernarvon Shire by Lewis Morris names the body of the peninsula "CREUDDYN" but applies the name "Orme's Head" to the headland's north-westerly seaward point. The first series Ordnance Survey map (published in 1841 and before the establishment of Llandudno) follows this convention. The headland is called the "Great Orme's Head" but its landward features all have Welsh names. It is likely that Orme became established as its common name due to Llandudno's burgeoning tourist trade because a majority of visitors and holidaymakers arrived by sea. The headland was the first sight of their destination in the three-hour journey from Liverpool by paddle steamer.

Parts of the Great Orme are managed as a nature reserve by the Conwy County Borough Countryside Service. The area, which is two miles (three kilometres) long by 1 mile (1.5 kilometres) wide, has a number of protective designations including Special Area of Conservation, Heritage Coast, Country Park, and Site of Special Scientific Interest. The local authority provides a warden service on the Great Orme that regularly patrols the special scientific and conservation areas. There are numerous maintained paths for walking to the summit; a section of the long-distance North Wales Path also crosses the headland. About half the Great Orme is in use as farmland, mostly for sheep grazing. In 2015, the National Trust purchased the summit's 140-acre (57-hectare) Parc Farm for £1million.

The Great Orme is a peninsula made mostly of limestone and dolomite, formed during the Early Carboniferous part of the Earth's geological history. Most of the Great Orme's rocks are between 339 and 326 million years old. The upper surface of the Great Orme is particularly noted for its limestone pavements covering several headland areas. There are also rich seams of dolomite-hosted copper ore. The Great Orme copper mine was estimated to have produced enough copper to make about 2,000 tons of bronze during the Bronze Age. The slopes of the Great Orme are subject to occasional subsidence.

Natural wells were greatly prized in limestone districts and the Great Orme was no exception. Water was required for copper mining purposes as well as for domestic and agricultural use. The following Great Orme wells are known and most still supply running water:

The Great Orme has a very rich flora, including most notably the only known site of the critically endangered wild cotoneaster (Cotoneaster cambricus), of which only six wild plants are known. Many of the flowers growing in shallow lime-rich earth on the headland have developed from the alpine sub-Arctic species that developed following the last ice-age. Spring and early summer flowers include bloody cranesbill, thrift and sea campion, clinging to the sheer rock face, while pyramidal orchid, common rockrose and wild thyme carpet the grassland. The old mines and quarries also provide suitable habitat for species of plants including spring squill growing on the old copper workings. The white horehound (Marrubium vulgare), which is found growing on the westernmost slopes of the Orme is said to have been used, and perhaps cultivated, by 14th-century monks, no doubt to make herbal remedies including cough mixtures. The rare horehound plume moth (Wheeleria spilodactylus) lays her eggs amongst the silky leaves and its caterpillars rely for food solely upon this one plant.