Historically, the peninsula was travelled by pilgrims en route to Bardsey Island (Welsh: Ynys Enlli), and its relative isolation has helped to conserve the Welsh language and culture, for which the locality is now famous. This perceived remoteness from urban life has lent the area an unspoilt image which has made Llŷn a popular destination for both tourists and holiday home owners. Holiday homes remain a bone of contention among locals, many of whom are priced out of the housing market by incomers. From the 1970s to the 1990s, a shadowy group known as Meibion Glyndŵr claimed responsibility for several hundred arson attacks on holiday homes using incendiary devices, some of which took place in Llŷn.
The name Llŷn is also sometimes spelled Lleyn, although this spelling is now less common and is generally considered to be an anglicisation. The name is thought to be of Irish origin, and to have the same root – Laigin (Laighin) in Irish – as the word Leinster and which also occurs in Porth Dinllaen on the north coast.
Following the death of Owain Whitetooth (Ddantgwyn), king of Gwynedd, Owain's son Saint Einion seems to have ruled Llŷn as a kingdom separate from his brother Cuneglas' kingdom in Rhos. He is credited with having sponsored Saint Cadfan's monastery on Bardsey Island, which became a major centre of pilgrimage during medieval times. There are numerous wells throughout the peninsula, many dating back to the pre-Christian era. Many have holy connotations and they were important stops for pilgrims heading to the island.
The most rural parts are characterised by small houses, cottages and individual farms, resembling parts of south west Ireland. There are small compact villages, built of traditional materials. The only large-scale industrial activities were quarrying and mining, which have now largely ceased. The granite quarries of northern Llŷn have left a legacy of inclines and export docks, and were the reason for the growth of villages such as Llithfaen and Trefor. Copper, zinc and lead were mined around Llanengan, while 196,770 long tons (199,930 t) of manganese were produced at Y Rhiw between 1894 and 1945. Shipbuilding was important at Nefyn, Aberdaron, Abersoch and Llanaelhaearn, although the industry collapsed after the introduction of steel ships from 1880. Nefyn was also an important herring port, and most coastal communities fished for crab and lobster.
Farming was originally simple and organic, but underwent major changes after the Second World War as machines came into widespread use. Land was drained and fields expanded and reseeded. From the 1950s onwards, extensive use was made of artificial fertilizers, herbicides and pesticides, leading to drastic changes in the appearance of the landscape.
Tourism developed after the railway to Pwllheli was built in 1867. The town expanded rapidly, with several large houses and hotels constructed, and a tramway was built linking the town to Llanbedrog. After the Second World War, Butlins established a holiday camp at Penychain, which attracted visitors from the industrial cities of North West England and the West Midlands. As car ownership increased, the tourist industry spread to the countryside and to coastal villages such as Aberdaron, Abersoch, Llanbedrog and Nefyn, where many families supplemented their income by letting out rooms and houses.