Llanfairpwllgwyngyllgogerychwyrndrobwllllantysiliogogogoch

Llanfairpwllgwyngyll (long form Llanfairpwllgwyngyllgogerychwyrndrobwllllantysiliogogogoch), also spelt Llanfair Pwllgwyngyll and commonly known as Llanfair PG or Llanfairpwll, is a village and community on the island of Anglesey in Wales, situated on the Menai Strait next to Menai Bridge and across the strait from Bangor. According to the 2001 census, the population of the community is 3,040, 76% of whom speak Welsh fluently; the highest percentage of speakers is in the 10-14 age group, where 97.1% are able to speak Welsh. It is the fifth largest settlement on the island in terms of population.

The long form of the name is the longest officially recognised place name in the United Kingdom and one of the longest in the world, being 58 letters in length (51 letters in the Welsh alphabet, where "ch" and "ll" count as single letters). The name is Welsh for "St Mary's church in the hollow of the white hazel near to the rapid whirlpool and the church of St Tysilio of the red cave".

This village was originally known as Llanfair Pwllgwyngyll (and is sometimes still referred to as Llanfairpwllgwyngyll) and was given its long name in the 19th century in an attempt to develop the village as a commercial and tourist centre (see Significance of the name below). Today the village is still signposted as Llanfairpwllgwyngyll, marked on Ordnance Survey maps as Llanfair Pwllgwyngyll and is known to locals as Llanfairpwll or simply Llanfair.

The name is also seen shortened to Llanfair PG, which is sufficient to distinguish it from the many other Welsh villages with Llanfair in their names. Other variant forms use the full name but with tysilio mutated to dysilio, and/or with a hyphen between drobwll and llan. In Welsh, the initial Ll may be mutated to a single L in some contexts.

Visitors stop at the railway station to be photographed next to the station sign, visit the nearby Visitors' Centre, or have 'passports' stamped at a local shop. Another tourist attraction is the nearby Marquess of Anglesey's Column, which at a height of 27 metres offers views over Anglesey and the Menai Strait. Designed by Thomas Harrison, the monument celebrates the heroism of Henry Paget, 1st Marquess of Anglesey at the Battle of Waterloo.